Remove skipping of several tests on NVIDIA since they are now passing.

  - MissingReturnStructOfArrays
  - DrawWithLevelsOutsideRangeWithInconsistentDimensions
  - TextureFormatChangesWithBaseLevel
  - TextureLuminance16Implicit

BUG=angleproject:3849
BUG=angleproject:1305
BUG=angleproject:596

Change-Id: Ie3c3ba6634a251a7320a61c6c4cc03cb178db925
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1763964Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>