Remove obsolete valgrind suppression

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 # running overnight and removing outdated bugs/suppressions.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 4490 matching lines @@
    fun:_ZN7WebCore9RenderBox14styleDidChangeENS_15StyleDifferenceEPKNS_11RenderStyleE
 }
 {
    bug_175100
    Memcheck:Leak
    ...
    fun:_ZN20OneClickSigninHelper14DidStopLoadingEPN7content14RenderViewHostE
    fun:_ZN*OneClickSigninHelperTest*
 }
 {
-   bug_175815
-   Memcheck:Leak
-   fun:_Znw*
-   fun:_ZN4base5Value18CreateIntegerValueEi
-   fun:_ZNK4base16FundamentalValue8DeepCopyEv
-   fun:_ZN4base8internal12_GLOBAL__N_125DictionaryHiddenRootValue26RemoveWithoutPathExpansionERKSsPPNS_5ValueE
-   fun:_ZN4base15DictionaryValue6RemoveERKSsPPNS_5ValueE
-   fun:_ZN32PluginFinderTest_JsonSyntax_Test8TestBodyEv
-}
-{
    bug_175823
    Memcheck:Leak
    ...
    fun:_ZN18ValueStoreFrontend*
 }
 {
     bug_175985
     Memcheck:Uninitialized
     fun:_ZN2cc13LayerTreeHost13setDebugStateERKNS_19LayerTreeDebugStateE
     ...
@@ skipping 1716 matching lines @@
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN4base8internal20PostTaskAndReplyImpl16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEESA_
    fun:_ZN4base10WorkerPool16PostTaskAndReplyERKN15tracked_objects8LocationERKNS_8CallbackIFvvEEES9_b
    fun:_ZN3net16HostResolverImpl16LoopbackProbeJobC2ERKN4base7WeakPtrIS0_EE
    fun:_ZN3net16HostResolverImplC1ERKNS_12HostResolver7OptionsEPNS_6NetLogE
    fun:_ZN8chromeos24HostResolverImplChromeOSC1E13scoped_refptrIN4base16MessageLoopProxyEEPNS_19NetworkStateHandlerERKN3net12HostResolver7OptionsEPNS7_6NetLogE
    fun:_ZN8chromeos24HostResolverImplChromeOS25CreateHostResolverForTestE13scoped_refptrIN4base16MessageLoopProxyEEPNS_19NetworkStateHandlerE
    fun:_ZN28HostResolverImplChromeOSTest22InitializeHostResolverEv
 }