ISurfaceComposer: rename isColorManagementUsed()

Rename isColorManagementUsed() to getColorManagement()
to follow the convention in ISurfaceComposer.

Test: adb shell /data/nativetest64/SurfaceFlinger_test/SurfaceFlinger_test --gtest_filter=LayerTransactionTest.SetColorTransformBasic
Change-Id: I63f75a98dbd230375f215a109a725672353eceef