Fix RenderTextTest.PangoAttributes test leaks; remove suppressions.

tools/heapcheck/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 # running overnight and removing outdated bugs/suppressions.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 1786 matching lines @@
    fun:AutofillPopupControllerUnitTest::AutofillPopupControllerUnitTest
    fun:AutofillPopupControllerUnitTest_GrowPopupInSpace_Test::AutofillPopupControllerUnitTest_GrowPopupInSpace_Test
    fun:testing::internal::TestFactoryImpl::CreateTest
 }
 {
    bug_171983
    Heapcheck:Leak
    ...
    fun:chromeos::MagnificationManagerTest_MagnificationObserver_Test::TestBody
 }
-{
-   bug_173597_a
-   Heapcheck:Leak
-   fun:g_realloc
-   fun:gfx::RenderTextTest_PangoAttributes_Test::TestBody
-}
-{
-   bug_173597_b
-   Heapcheck:Leak
-   fun:??
-   fun:gfx::RenderTextTest_PangoAttributes_Test::TestBody
-}
-{
-   bug_173597_c
-   Heapcheck:Leak
-   fun:FcConfigEvaluate
-   fun:gfx::RenderTextLinux::EnsureLayout
-   fun:gfx::RenderTextTest_PangoAttributes_Test::TestBody
-}