Remove handling of the unitTestInject* bits in base MTRDevice. #91288

Job	Run time
Build framework (macos-release, -sdk macosx -configuration Release)	21m 53s
Build framework (macos-release, -sdk macosx -configuration Release)	21m 53s
Build framework (ios-release, -sdk iphoneos -configuration Release)	10m 9s
Build framework (ios-release, -sdk iphoneos -configuration Release)	10m 9s
Build framework (tvos-debug, -sdk appletvos -configuration Debug)	9m 26s
Build framework (tvos-debug, -sdk appletvos -configuration Debug)	9m 26s
Build framework (watchos-debug, -sdk watchos -configuration Debug)	13m 19s
Build framework (watchos-debug, -sdk watchos -configuration Debug)	13m 19s
Run framework tests (asan, -enableAddressSanitizer YES -enableUndefinedBehaviorSanitizer YES)	27m 19s
Run framework tests (asan, -enableAddressSanitizer YES -enableUndefinedBehaviorSanitizer YES)	27m 19s
Run framework tests (tsan, -enableThreadSanitizer YES)	42m 22s
Run framework tests (tsan, -enableThreadSanitizer YES)	31m 1s
Run framework tests (leaks, ENABLE_LEAK_DETECTION=1)	38m 23s
Run framework tests (leaks, ENABLE_LEAK_DETECTION=1)	38m 23s
	5h 14m 21s

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