ZBXNEXT-3185 implemented custom parameter definitions for alertscripts.
by default, no parameters are added, thus it requires for the user to look them up in the manual.
several users have also been confused about these parameters and wondered why their scripts get no data passed.

it is suggested to have 3 parameters specified by default, with {ALERT.SENDTO}, {ALERT.SUBJECT} and {ALERT.MESSAGE} filled in.

it is much easier to remove them if not needed than adding, which requires knowing the exact names