Valgrind: Remove an unused suppression for MHTML code.

tools/valgrind/memcheck/suppressions.txt

 # There are four kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 1328 matching lines @@
    ...
    fun:_swrast_Triangle
    fun:triangle_rgba
    ...
    fun:run_render
    fun:_tnl_run_pipeline
    fun:_tnl_draw_prims
    fun:_tnl_vbo_draw_prims
 }
 {
-   bug_122457
-   Memcheck:Leak
-   fun:malloc
-   fun:_ZN3WTF10fastMallocEm
-   fun:_ZN3WTF10RefCountedIN5blink12MHTMLArchiveEEnwEm
-   fun:_ZN5blink12MHTMLArchive6createEv
-   ...
-   fun:_ZN5blink11MHTMLParser22parseArchiveWithHeaderEPNS_10MIMEHeaderE
-   fun:_ZN5blink11MHTMLParser12parseArchiveEv
-   fun:_ZN5blink12MHTMLArchive6createERKNS_4KURLEPNS_12SharedBufferE
-}
-{
    bug_122717_use_after_free
    Memcheck:Unaddressable
    fun:__pthread_mutex_unlock_usercnt
    fun:_ZN4base8internal8LockImpl6UnlockEv
    fun:_ZN4base4Lock7ReleaseEv
    fun:_ZN4base8AutoLockD1Ev
    fun:_ZN5gdata15GDataFileSystem21RunTaskOnIOThreadPoolERKN4base8CallbackIFvvEEE
 }
 {
    bug_122717_leak
@@ skipping 2061 matching lines @@
    ...
    fun:_ZN7content28ShellURLRequestContextGetter20GetURLRequestContextEv
    fun:_ZN7content21ChromeAppCacheService20InitializeOnIOThreadERKN4base8FilePathEPNS_15ResourceContextEPN3net23URLRequestContextGetterE13scoped_refptrIN7storage20SpecialStoragePolicyEE
 }
 {
    bug_587544_b
    Memcheck:Leak
    ...
    fun:_ZN4base4BindIMN7content21ChromeAppCacheServiceEFvRKNS_8FilePathEPNS1_15ResourceContextEPN3net23URLRequestContextGetterE13scoped_refptrIN7storage20SpecialStoragePolicyEEEJPS2_S3_S7_SB_IS9_ESE_EEENS_8CallbackINS_8internal22MakeUnboundRunTypeImplIT_JDpT0_EE4TypeEEESM_DpOSN_
 }