Revert of Implement SkImageFilter::Cache with SkResourceCache. (patchset #8 id:140001 of https://codereview.chromium.org/1370323002/ )

Reason for revert:
Landed PS8 temporarily to trigger the perf bots.

Original issue's description:
> Implement SkImageFilter::Cache with SkResourceCache.
>
> The single global cache now uses the global SkResourceCache,
> and any Create()ed cache uses a local SkResourceCache.
>
> No real public API changes (and only deletes).
>
> I don't see any pixel diffs on .skps or GMs.
> Don't see any significant perf difference on 8888 or gpu configs.
> DM peak memory usage did drop by about 113M, close to the 128M cache size.
>
> BUG=skia:3662
>
> Landing PS8 temporarily to trigger the perf bots.
> TBR=reed@google.com
>
> Committed: https://skia.googlesource.com/skia/+/75135d8ae1aa12e8e6bfce63291e5e876a77546f

TBR=reed@google.com,robertphillips@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:3662

Review URL: https://codereview.chromium.org/1381523002
diff --git a/src/core/SkResourceCache.cpp b/src/core/SkResourceCache.cpp
index a79c953..54091f1 100644
--- a/src/core/SkResourceCache.cpp
+++ b/src/core/SkResourceCache.cpp
@@ -658,6 +658,7 @@
 }
 
 void SkGraphics::PurgeResourceCache() {
+    SkImageFilter::PurgeCache();
     return SkResourceCache::PurgeAll();
 }