Do not use hard-coded apex name

libinput checks input_device.config_file.apex sysprop when loading input
config.

This removes hard-coded apex name (com.android.input.config).

Bug: 315080500
Test: adb shell dumpsys input
  # set "touch.orientationAware = 0" in Touchscreen_0.idc
  # build/install the input config apex
  # Observe the Input configuration
  # "Touch Input Mapper" shows "OrientationAware: false"
Change-Id: I4e0415f26397f4ec4d77ee1d1909da47a04b986a