Remove unused locks in mus ContextProvider classes

components/mus/public/cpp/context_provider.h

Index: components/mus/public/cpp/context_provider.h
diff --git a/components/mus/public/cpp/context_provider.h b/components/mus/public/cpp/context_provider.h
index 973aa7a71254f4686b99ee37b5d425bc5824c103..8b4ed0833217006e42ebc64716bedb4983aa875b 100644
--- a/components/mus/public/cpp/context_provider.h
+++ b/components/mus/public/cpp/context_provider.h
@@ -10,7 +10,6 @@
 #include <memory>
 
 #include "base/macros.h"
-#include "base/synchronization/lock.h"
 #include "cc/output/context_provider.h"
 #include "mojo/public/c/gles2/gles2_types.h"
 #include "mojo/public/cpp/system/core.h"
@@ -48,8 +47,6 @@ class ContextProvider : public cc::ContextProvider {
   MojoGLES2Context context_;
   std::unique_ptr<gpu::gles2::GLES2Interface> context_gl_;
 
-  base::Lock context_lock_;
-
   DISALLOW_COPY_AND_ASSIGN(ContextProvider);
 };