Revert of Add a mutex to GrContext::readSurfacePixels to protect against multiple CPU raster threads accessin…

src/gpu/GrContext.cpp

Index: src/gpu/GrContext.cpp
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index c6fe6c23d30ad030ae3c077ee014529fa31879ea..4e8060b1877872773106235d970943d0bda6853d 100644
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -460,7 +460,7 @@
     RETURN_FALSE_IF_ABANDONED
     ASSERT_OWNED_RESOURCE(src);
     SkASSERT(src);
-    SkAutoMutexAcquire ama(fReadPixelsMutex);
+
     // Adjust the params so that if we wind up using an intermediate surface we've already done
     // all the trimming and the temporary can be the min size required.
     if (!GrSurfacePriv::AdjustReadPixelParams(src->width(), src->height(),