remove remnants of 10.0 bugfix, incorrectly merged into 10.2
Using col_names[i] was obviously, wrong, must've been col_names[ifield->col_no].
incorrect column name resulted in innodb having index unique_id2(id1),
while the server thought it's unique_id2(id4).
But col_names[ifield->col_no] is wrong too, because `table` has non-renamed
columns, so the correct column name is always dict_table_get_col_name(table, ifield->col_no)
automatic shortening of a too-long non-unique key should
be not a warning, but a note. It's a normal optimization,
doesn't affect correctness, and should never be converted to
an error, no matter how strict sql_mode is.
