Remove a suppression for an uninitialized read in old CSS flexbox.

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 # running overnight and removing outdated bugs/suppressions.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 5566 matching lines @@
 {
    bug_130619
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN7WebCore9ClipRects6createERKS0_
    fun:_ZN7WebCore11RenderLayer15updateClipRectsEPKS0_PNS_12RenderRegionENS_13ClipRectsTypeENS_29OverlayScrollbarSizeRelevancyE
    ...
    fun:_ZNK7WebCore11RenderLayer15parentClipRectsEPKS0_PNS_12RenderRegionENS_13ClipRectsTypeERNS_9ClipRectsENS_29OverlayScrollbarSizeRelevancyE
    fun:_ZNK7WebCore11RenderLayer18backgroundClipRectEPKS0_PNS_12RenderRegionENS_13ClipRectsTypeENS_29OverlayScrollbarSizeRelevancyE
 }
-{
-   bug_131351
-   Memcheck:Uninitialized
-   ...
-   fun:_ZN7WebCore15FlexBoxIterator4nextEv
-   ...
-   fun:_ZN7WebCore27RenderDeprecatedFlexibleBox19layoutHorizontalBoxEb
-   fun:_ZN7WebCore27RenderDeprecatedFlexibleBox11layoutBlockEbNS_20FractionalLayoutUnitE
-   ...
-   fun:_ZN7WebCore11RenderBlock6layoutEv
-   fun:_ZN7WebCore10RenderView6layoutEv
-   fun:_ZN7WebCore9FrameView6layoutEb
-}
 
 #-----------------------------------------------------------------------
 # 4. These only occur on our Google workstations
 
 {
    bug_todo_getdelim
    Memcheck:Leak
    fun:malloc
    fun:getdelim
    ...
    fun:call_init
    fun:_dl_init
 }
 {
    bug_todo_getdelim2
    Memcheck:Leak
    fun:malloc
    fun:getdelim
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
 }
 {
    bug_todo_grep
    Memcheck:Leak
    fun:malloc
    obj:/bin/grep
    obj:/bin/grep
 }