qcacmn: Remove unused peer mgmt stats

Peer delete request and response stats has been moved to per vap
stats. The time info on assoc, disassoc and deauth was already
cleaned up, but members in the dp_peer struct weren't removed.

Change-Id: Ie4a1b171178d8ad03abd76069cc0777802814993
CRs-Fixed: 2451766
3 files changed