strbuf: simplify strbuf_expand_literal_cb()

Now that strbuf_expand_literal_cb() is no longer used as a callback,
drop its "_cb" name suffix and unused context parameter.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.h

@@ -320,11 +320,9 @@ const char *strbuf_join_argv(struct strbuf *buf, int argc,
 /**
  * Used with `strbuf_expand_step` to expand the literals %n and %x
  * followed by two hexadecimal digits. Returns the number of recognized
- * characters. The context argument is ignored.
+ * characters.
  */
-size_t strbuf_expand_literal_cb(struct strbuf *sb,
-				const char *placeholder,
-				void *context);
+size_t strbuf_expand_literal(struct strbuf *sb, const char *placeholder);
 
 /**
  * If the string pointed to by `formatp` contains a percent sign ("%"),