dovecot: fix deprecated keys in plist
dovecot: fix deprecated keys in plist

The "OnDemand" and "ServiceDescription" were deprecated in OS X 10.5.
Replace "OnDemand" with "KeepAlive" and delete the "ServiceDescription" key.

Closes #43775.

Signed-off-by: Dominyk Tiller <53e438f55903875d07efdd98a8aaf887e7208dd3@gmail.com>

kwilczynski/homebrew,kwilczynski/homebrew,kwilczynski/homebrew,kwilczynski/homebrew