Remove the api txt files for 28.

The others were removed in I004a02ed77533b1f2dafd02015a0e6f50b0d4da5,
but 28 conflict between aosp and internal.

Bug: 77525052
Test: make
Change-Id: I52e938cfad8485fe242693b9d107af4ecae41cf0
Merged-In: I52e938cfad8485fe242693b9d107af4ecae41cf0
2 files changed