Syntax:
DROP FUNCTION function_name

This statement drops the user-defined function (UDF) named
function_name.

To drop a function, you must have the DELETE privilege for the mysql
database. This is because DROP FUNCTION removes a row from the
mysql.func system table that records the function's name, type, and
shared library name.

URL: http://dev.mysql.com/doc/refman/5.1/en/drop-function-udf.html

