Enable implicit casting of VARCHAR and BIT args in aggregate functions

Default function implementations that that throw unsupported operation exceptions in the class AggregateErrorFunctions prevent the implicit casting of VARCHAR and BIT arguments to neighbouring types. E.g.

apache drill> select sum('1');
Error: UNSUPPORTED_OPERATION ERROR: Only COUNT, MIN and MAX aggregate functions supported for VarChar type

This issue proposes to remove AggregateErrorFunctions so that implicit casting works, the example above changing as follows.

apache drill> select sum('1');
EXPR$0  1
1 row selected (2.346 seconds)