Description: Revert "tty: n_gsm: fix UAF in gsm_cleanup_mux"
References:
Notes:
 carnil> Introduced in 9b9c8195f3f0 ("tty: n_gsm: fix UAF in gsm_cleanup_mux").
 carnil> Vulnerable versions: 5.10.190 5.10.198 5.15.124 5.15.134 6.1.43 6.1.56 6.4.8
 carnil> 6.5-rc4 6.5.6.
Bugs:
upstream: released (6.6-rc4) [29346e217b8ab8a52889b88f00b268278d6b7668]
6.7-upstream-stable: N/A "Fixed before branching point"
6.6-upstream-stable: N/A "Fixed before branching point"
6.1-upstream-stable: released (6.1.56) [c61d0b87a7028c2c10faffc524d748334c7b9827]
5.10-upstream-stable: released (5.10.198) [6d5c8862932d31a810b6545f7d69ecc124402c6e]
4.19-upstream-stable: N/A "Vulnerable code not present"
sid: released (6.5.6-1)
6.1-bookworm-security: released (6.1.64-1)
5.10-bullseye-security: released (5.10.205-1)
4.19-buster-security: N/A "Vulnerable code not present"