Remove out-of-date TODO comment.

This comment originally referred to a line that immediately followed it:
    SkTBlitterAllocator allocator;

which was passed to the SkMakeBitmapShader call that followed it. This
was added at http://review.skia.org/8140 and removed soon afterwards at
http://review.skia.org/8407, but the comment was not removed.

Change-Id: Iebe4b34de737abaf3aa7c769f466a21802d0807a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/418139
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

src/core/SkBitmapDevice.cpp

@@ -522,11 +522,6 @@ void SkBitmapDevice::drawImageRect(const SkImage* image, const SkRect* src, cons
 
     USE_SHADER:
 
-    // TODO(herb): Move this over to SkArenaAlloc when arena alloc has a facility to return sk_sps.
-    // Since the shader need only live for our stack-frame, pass in a custom allocator. This
-    // can save malloc calls, and signals to SkMakeBitmapShader to not try to copy the bitmap
-    // if its mutable, since that precaution is not needed (give the short lifetime of the shader).
-
     // construct a shader, so we can call drawRect with the dst
     auto s = SkMakeBitmapShaderForPaint(paint, *bitmapPtr, SkTileMode::kClamp, SkTileMode::kClamp,
                                         sampling, &matrix, kNever_SkCopyPixelsMode);