Remove SkThread.h, include SkMutex.h or SkAtomics.h as appropriate.

SkThread.h doesn't do anything anymore execept include those two,
and thankfully, it doesn't seem to be mentioned outside Skia.

No public API changes.
TBR=reed@google.com

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/c50acf2321d7a934c80d754e9cbe936dfb8eb4cc

Review URL: https://codereview.chromium.org/1215393002
diff --git a/tests/PathOpsExtendedTest.cpp b/tests/PathOpsExtendedTest.cpp
index df80f46..69a2d61 100644
--- a/tests/PathOpsExtendedTest.cpp
+++ b/tests/PathOpsExtendedTest.cpp
@@ -11,10 +11,10 @@
 #include "SkCanvas.h"
 #include "SkForceLinking.h"
 #include "SkMatrix.h"
+#include "SkMutex.h"
 #include "SkPaint.h"
 #include "SkRTConf.h"
 #include "SkStream.h"
-#include "SkThread.h"
 
 #ifdef SK_BUILD_FOR_MAC
 #include <sys/sysctl.h>