DeviceContextVkImpl: code cleanup #3944

Job	Run time
Linux -> Pre-checks	16s
Linux -> Clang-x64, Release	10m 55s
Linux -> Clang-NO_GLSLANG-NO_HLSL-x64, Release	6m 15s
Linux -> GCC-x64, Release	11m 2s
Linux -> Clang-NO_GLSLANG-x64, Debug	7m 51s
Linux -> Clang-x64, Debug	10m 53s
Linux -> GCC-x64, Debug	11m 47s
	58m 59s

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