sql: remove name overloading for SQL builtins

Now all SQL builtins are unique, i.e. each function has the only
hash table entry. This technique requires to remove static argc
checks for some builtins(substr, round, like, trim, count,
group_concat). Now they raise a runtime error in case of invalid
usage.

Updated error messages correspondingly, to provide more
informative messages in such cases. Taking into account upcoming
changes, all built-in functions names are uppercased.

Needed for #2200, #4113, #2233