Enotify: cleaned up method API.

TODO

src/lib-sieve/plugins/enotify/cmd-notify.c

src/lib-sieve/plugins/enotify/ext-enotify-common.c

src/lib-sieve/plugins/enotify/ext-enotify-common.h

src/lib-sieve/plugins/enotify/ntfy-mailto.c

src/lib-sieve/plugins/enotify/sieve-ext-enotify.h

src/lib-sieve/sieve-result.c

src/lib-sieve/sieve-result.h