Remove from docs references to obsolete MULE variables

* src/search.c (search_buffer): Remove obsolete text from a
comment.
* src/fns.c (Fstring_make_unibyte): Remove obsolete text from
a doc string.

src/fns.c

@@ -1042,10 +1042,8 @@ string the same way whether it is unibyte or multibyte.)  */)
 DEFUN ("string-make-unibyte", Fstring_make_unibyte, Sstring_make_unibyte,
        1, 1, 0,
        doc: /* Return the unibyte equivalent of STRING.
-Multibyte character codes are converted to unibyte according to
-`nonascii-translation-table' or, if that is nil, `nonascii-insert-offset'.
-If the lookup in the translation table fails, this function takes just
-the low 8 bits of each character.  */)
+Multibyte character codes above 255 are converted to unibyte
+by taking just the low 8 bits of each character's code.  */)
   (Lisp_Object string)
 {
   CHECK_STRING (string);

src/search.c

@@ -1341,12 +1341,7 @@ search_buffer (Lisp_Object string, ptrdiff_t pos, ptrdiff_t pos_byte,
 	}
       else
 	{
-	  /* Converting multibyte to single-byte.
-
-	     ??? Perhaps this conversion should be done in a special way
-	     by subtracting nonascii-insert-offset from each non-ASCII char,
-	     so that only the multibyte chars which really correspond to
-	     the chosen single-byte character set can possibly match.  */
+	  /* Converting multibyte to single-byte.  */
 	  raw_pattern_size = SCHARS (string);
 	  raw_pattern_size_byte = SCHARS (string);
 	  raw_pattern = SAFE_ALLOCA (raw_pattern_size + 1);