Fix missing update of certificate list after deleting keys

There was a race between automatic keylisting (triggered by filesystem
changes) and the manual removal of keys from the key cache. This race
is avoided by suspending automatic keylisting while keys are being deleted.

(cherry picked from commit af1b1ee0bad5df7bd87d3acb36771bd953821b74)

• GnuPG-bug-id: T7863