Remove strict-virtual-specifiers option, since it's enabled everywhere.

tools/clang/plugins/tests/base_refcounted.txt

 In file included from base_refcounted.cpp:5:
 ./base_refcounted.h:47:3: warning: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.
   ~PublicRefCountedDtorInHeader() {}
   ^
 ./base_refcounted.h:44:7: note: [chromium-style] 'PublicRefCountedDtorInHeader' inherits from 'base::RefCounted<PublicRefCountedDtorInHeader>' here
     : public base::RefCounted<PublicRefCountedDtorInHeader> {
       ^
 ./base_refcounted.h:59:3: warning: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.
   ~PublicRefCountedThreadSafeDtorInHeader() {}
   ^
 ./base_refcounted.h:55:7: note: [chromium-style] 'PublicRefCountedThreadSafeDtorInHeader' inherits from 'base::RefCountedThreadSafe<PublicRefCountedThreadSafeDtorInHeader>' here
     : public base::RefCountedThreadSafe<
       ^
 ./base_refcounted.h:73:3: warning: [chromium-style] Classes that are ref-counted and have non-private destructors should declare their destructor virtual.
   ~ProtectedRefCountedDtorInHeader() {}
   ^
 ./base_refcounted.h:110:3: warning: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.
-  virtual ~DerivedProtectedToPublicInHeader() {}
+  ~DerivedProtectedToPublicInHeader() override {}
   ^
 ./base_refcounted.h:107:7: note: [chromium-style] 'DerivedProtectedToPublicInHeader' inherits from 'ProtectedRefCountedVirtualDtorInHeader' here
     : public ProtectedRefCountedVirtualDtorInHeader {
       ^
 ./base_refcounted.h:81:7: note: [chromium-style] 'ProtectedRefCountedVirtualDtorInHeader' inherits from 'base::RefCounted<ProtectedRefCountedVirtualDtorInHeader>' here
     : public base::RefCounted<ProtectedRefCountedVirtualDtorInHeader> {
       ^
 ./base_refcounted.h:115:7: warning: [chromium-style] Classes that are ref-counted should have explicit destructors that are declared protected or private.
 class ImplicitDerivedProtectedToPublicInHeader
       ^
@@ skipping 25 matching lines @@
 class AnImplicitInterface {
       ^
 ./base_refcounted.h:165:7: note: [chromium-style] 'ImplementsAnImplicitInterface' inherits from 'AnImplicitInterface' here
     : public AnImplicitInterface,
       ^
 ./base_refcounted.h:204:3: warning: [chromium-style] Classes that are ref-counted and have non-private destructors should declare their destructor virtual.
   ~RefcountedType() {}
   ^
 ./base_refcounted.h:204:3: warning: [chromium-style] Classes that are ref-counted and have non-private destructors should declare their destructor virtual.
 base_refcounted.cpp:16:3: warning: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.
-  virtual ~AnonymousDerivedProtectedToPublicInImpl() {}
+  ~AnonymousDerivedProtectedToPublicInImpl() override {}
   ^
 base_refcounted.cpp:13:7: note: [chromium-style] 'AnonymousDerivedProtectedToPublicInImpl' inherits from 'ProtectedRefCountedVirtualDtorInHeader' here
     : public ProtectedRefCountedVirtualDtorInHeader {
       ^
 ./base_refcounted.h:81:7: note: [chromium-style] 'ProtectedRefCountedVirtualDtorInHeader' inherits from 'base::RefCounted<ProtectedRefCountedVirtualDtorInHeader>' here
     : public base::RefCounted<ProtectedRefCountedVirtualDtorInHeader> {
       ^
 ./base_refcounted.h:73:3: warning: [chromium-style] Classes that are ref-counted and have non-private destructors should declare their destructor virtual.
   ~ProtectedRefCountedDtorInHeader() {}
   ^
 base_refcounted.cpp:33:3: warning: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.
   ~PublicRefCountedDtorInImpl() {}
   ^
 base_refcounted.cpp:30:7: note: [chromium-style] 'PublicRefCountedDtorInImpl' inherits from 'base::RefCounted<PublicRefCountedDtorInImpl>' here
     : public base::RefCounted<PublicRefCountedDtorInImpl> {
       ^
 base_refcounted.cpp:59:3: warning: [chromium-style] Classes that are ref-counted should have destructors that are declared protected or private.
   ~UnsafeTypedefChainInImpl() {}
   ^
 base_refcounted.cpp:56:34: note: [chromium-style] 'UnsafeTypedefChainInImpl' inherits from 'Baz::MyLocalTypedef' (aka 'RefCounted<Foo::BarInterface>') here
 class UnsafeTypedefChainInImpl : public Baz::MyLocalTypedef {
                                  ^
 13 warnings generated.