Remove deprecated alias of test decorators (2/2)

The attr decorator was deprecated during Pike cycle[1] and multiple
cycles have passed since then.

[1] 3b46d27c90aa6289724f4c137a0838c89d116b62

Depends-on: https://review.opendev.org/908551
Change-Id: Ib24acdd68d1639cd0353f40db1bc9a32b3cecae8
2 files changed