mail: Rename mail synchronization script to mail-sync

Since we do not use neomutt anymore. Additionally, perhaps a 'mail-'
prefixed system is better for scripts etc which run independent of a
specific MUA.

office/.config/aerc/accounts.conf

@@ -4,7 +4,7 @@ maildir-store             = ~/documents/mail
 query-map                 = ~/.config/aerc/Personal.qmap
 default                   = Inbox
 folders-sort              = Inbox,Drafts,Sent
-check-mail-cmd            = neomutt-syncmail
+check-mail-cmd            = mail-sync
 exclude-tags              = spam
 multi-file-strategy       = act-dir-delete-rest
 restrict-delete           = true