Delete callbacks after use in canned browsing data helpers.

tools/valgrind/memcheck/suppressions.txt

 # There are three 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 # running overnight and removing outdated bugs/suppressions.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 3972 matching lines @@
 }
 {
    bug_51679
    Memcheck:Leak
    fun:_Znw*
    ...
    fun:_ZN23ExtensionMessageService16AddEventListenerERKSsi
    fun:_ZN24BrowserRenderProcessHost22OnExtensionAddListenerERKSs
    fun:_Z16DispatchToMethodI24BrowserRenderProcessHostMS0_FvRKSsESsEvPT_T0_RK6Tuple1IT1_E
 }
-{
-   bug_51707
-   Memcheck:Leak
-   fun:_Znw*
-   fun:_ZN16CookiesTreeModelC2EPN3net13CookieMonsterEP26BrowsingDataDatabaseHelperP30BrowsingDataLocalStorageHelperS6_P26BrowsingDataAppCacheHelper
-   fun:_ZN26TabSpecificContentSettings27LocalSharedObjectsContainer19GetCookiesTreeModelEv
-   fun:-[CollectedCookiesWindowController loadTreeModelFromTabContents]
-   fun:-[CollectedCookiesWindowController initWithTabContents:]
-   fun:_ZN12_GLOBAL__N_154CollectedCookiesWindowControllerTest_Construction_Test8TestBodyEv
-}