Remove HID usage mapping for stylus buttons in Generic.kl

... until we figure out a way to determine if a device supports a
specific HID usage code. Right now, having a usage code mapping means we
automatically assume the device can report the key code. Assuming a
device can support a stylus keycode makes the device get classified as a
stylus, leading to widespread misclassifications.

Bug: 291529805
Test: atest inputflinger_tests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5fb192aaec7a1d4ebb1384d96b3f79d4b2ca2f2c)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:55930e07d69fbd8ffd27d677a06fd0ba71a30bf8)
Merged-In: I580514bdcbbfbe93df83fa3faa6262077e881243
Change-Id: I580514bdcbbfbe93df83fa3faa6262077e881243