audioserver: remove flag "fix_aaudio_stream_reopen_in_libaudiohal_aidl"

The fix for the bug ended up not requiring the flag.

Bug: 274456992
Bug: 409369453
Test: N/A
Flag: EXEMPT removing fix_aaudio_stream_reopen_in_libaudiohal_aidl
Change-Id: I45d55a1ca8a302da507f49dba449e48d3a94fb78