Fix Clang warning in release about unused variables.

The latest version of Clang correctly detects that these variables
are unused in a release build.

Change-Id: I155104bd181816e9cb18a954830398d56cf6192b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/842499
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
1 file changed