Fix ICU locale option handling in CREATE DATABASE

The code took the LOCALE option as the default/fallback for
ICU_LOCALE, but this was neither documented nor intended, so remove
it.  (It was probably left in from an earlier patch version.)

Reported-by: Marina Polyakova <m.polyakova@postgrespro.ru>
Discussion: https://www.postgresql.org/message-id/flat/f385ba25e7f8be427b8c582e5cca7d79%40postgrespro.ru#515a31c5429d6d37ad1d5c9d66962a1e

Author: petere

src/backend/commands/dbcommands.c

@@ -912,11 +912,6 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 				 errmsg("ICU locale cannot be specified unless locale provider is ICU")));
-	if (dblocprovider == COLLPROVIDER_ICU && !dbiculocale)
-	{
-		if (dlocale && dlocale->arg)
-			dbiculocale = defGetString(dlocale);
-	}
 	if (distemplate && distemplate->arg)
 		dbistemplate = defGetBoolean(distemplate);
 	if (dallowconnections && dallowconnections->arg)