Revert "Opt into new image-shaders with sampling"

This reverts commit c957bfbe2c.

Reason for revert: needed for flutter

Original change's description:
> Opt into new image-shaders with sampling
>
> Change-Id: I2d48046f68eb25a12c0c0ce4fb7cd285e53a5c21
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/372036
> Reviewed-by: Mike Reed <reed@google.com>
> Commit-Queue: Mike Reed <reed@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I1a3271988a3b4f6be03f7fe6f58f0e75086849da
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/372977
Reviewed-by: Mike Reed <reed@google.com>

gn/flutter_defines.gni

@@ -15,6 +15,7 @@ flutter_defines = [
   "SK_PARAGRAPH_LIBTXT_SPACES_RESOLUTION",
 
   # Staging
+  "SK_SUPPORT_LEGACY_IMPLICIT_FILTERQUALITY",
 
   # Fast low-precision software rendering isn't a priority for Flutter.
   "SK_DISABLE_LEGACY_SHADERCONTEXT",