Update GPU unit tests to identify an enforced CTS version level

Cherry-pick to T.

SkDSLRuntimeEffectTest.cpp:
- This test does not exist in later branches. Update its call to
DEF_GPUTEST_FOR_RENDERING_CONTEXTS to pass a CtsEnforcement value.

skqp.cpp:
- Remove unused read_lines.

tests/SkSLTest.cpp
- Remove tests that were accidentally introduced by the cherry-pick.
These tests require .sksl files which don't exist in the old branch.
Moreover, without the commits that introduce them, they may not pass.
- Switch RecursiveComparison back to CPU only.

tests/Test.h:
- Switch skgpu::graphite::Context back to skgpu::Context to match T.

Conflicts:
	platform_tools/android/apps/skqp/src/main/assets/skqp/unittests.txt
	tests/ColorFilterTest.cpp
	tests/GrGpuBufferTest.cpp
	tests/SkRuntimeEffectTest.cpp
	tests/SkSLTest.cpp
	tests/Test.h
	tools/skqp/src/skqp.cpp

Bug: b/240427374
Bug: b/269703382
Change-Id: Ida2c58a30c70d9a4ae0f64ec943662ba1162e406
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/703876
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>