Revert "Only include header once in combined MSL shader."

This reverts commit e7a8f85e4f224d49323689a346e68196b40b7d65.

Reason for revert: must revert dependent CL

Original change's description:
> Only include header once in combined MSL shader.
>
> Bug: skia:11389
> Change-Id: I3e24dcaa2cfeddc7efd7985f9f42a59bfc8175f2
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/385137
> Reviewed-by: John Stiles <johnstiles@google.com>
> Commit-Queue: Jim Van Verth <jvanverth@google.com>

TBR=jvanverth@google.com,johnstiles@google.com

Change-Id: I7a886b6c57a666e54e65365e41dcb57bd9ab4ba6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:11389
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/385237
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
234 files changed