(partially) Fix Bug#55227 Fix compiler warnings in innodb with gcc 4.6

Fix compiler warning:
handler/ha_innodb.cc: In function 'void innobase_drop_database(handlerton*, char*)':
handler/ha_innodb.cc:7010:6: error: variable 'error' set but not used [-Werror=unused-but-set-variable]

storage/innodb_plugin/handler/ha_innodb.cc

@@ -7007,7 +7007,6 @@ innobase_drop_database(
 	ulint	len		= 0;
 	trx_t*	trx;
 	char*	ptr;
-	int	error;
 	char*	namebuf;
 	THD*	thd		= current_thd;
 
@@ -7050,7 +7049,7 @@ innobase_drop_database(
 #else
 	trx = innobase_trx_allocate(thd);
 #endif
-	error = row_drop_database_for_mysql(namebuf, trx);
+	row_drop_database_for_mysql(namebuf, trx);
 	my_free(namebuf, MYF(0));
 
 	/* Flush the log to reduce probability that the .frm files and