Remove unused class GrDDLGpu

Change-Id: I66c0bb988e187cb6be43b2d2a726023b0bb25b69
Reviewed-on: https://skia-review.googlesource.com/105764
Reviewed-by: Greg Daniel <egdaniel@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
4 files changed