macro.c: use string hash from hash.h for macro_hash

Another case of duplicated hash.h code, the only minor difference
being that macro->format_hash was created with 7 entries vs. str_hash
with 16 entries.

	* macro.c (macro_init, define_macro): Use str_htab_create.
	(do_formals, define_macro, macro_expand_body): Use str_hash_insert
	(macro_expand_body): Use str_hash_find and str_hash_delete.
	(delete_macro): Likewise.
	(sub_actual, macro_expand, check_macro): Use str_hash_find.
	(expand_irp): Use str_htab_create and str_hash_insert.
	* macro.h (struct macro_struct): Tidy.
	(struct macro_hash_entry, macro_hash_entry_t, hash_macro_entry),
	(eq_macro_entry, macro_entry_alloc, macro_entry_find),
	(struct formal_hash_entry, formal_hash_entry_t),
	(hash_formal_entry, eq_formal_entry, formal_entry_alloc),
	(formal_entry_find): Delete.
	* config/tc-iq2000.c (iq2000_add_macro): Use str_htab_create
	and str_hash_insert.