[][MAC80211][misc][Change revert patch for backports-5.15]

[Description]
Change revert patch for backports-5.15
Since mt7996 already merge into mt76 master tree, remove temp mt7996 source code.

[Release-log]
N/A

Change-Id: I28ec1a2b7ddf24b000bd05db5aee140d96a5a03d
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6916254
271 files changed