CapturedTouchpadEventConverter: clean up relative axes flag

This is now launched, so we can safely remove it.

Bug: 374937381
Test: atest --host inputflinger_tests:CapturedTouchpadEventConverterTest
Test: atest CtsHardwareTestCases:android.hardware.input.cts.tests.SonyDualshock4BluetoothTest
Flag: EXEMPT removing
      com.android.input.flags.include_relative_axis_values_for_captured_touchpads
Change-Id: I98912368cab71c8bb8691228e1e8dcab4e491634