crypto: af_alg - get rid of alg_memory_allocated

alg_memory_allocated does not seem to be really used.

alg_proto does have a .memory_allocated field, but no
corresponding .sysctl_mem.

This means sk_has_account() returns true, but all sk_prot_mem_limits()
users will trigger a NULL dereference [1].

THis was not a problem until SO_RESERVE_MEM addition.

general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 1 PID: 3591 Comm: syz-executor153 Not tainted 5.17.0-rc3-syzkaller-00316-gb81b1829e7e3 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:sk_prot_mem_limits include/net/sock.h:1523 [inline]
RIP: 0010:sock_reserve_memory+0x1d7/0x330 net/core/sock.c:1000
Code: 08 00 74 08 48 89 ef e8 27 20 bb f9 4c 03 7c 24 10 48 8b 6d 00 48 83 c5 08 48 89 e8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <80> 3c 08 00 74 08 48 89 ef e8 fb 1f bb f...