patch 8.0.1056: cannot build with +diff but without +multi_byte

Problem:    Cannot build with the diff feature but without the mutli-byte
            feature.
Solution:   Remove #ifdefs. (John Marriott)

src/diff.c

@@ -1702,9 +1702,7 @@ diff_equal_char(char_u *p1, char_u *p2, int *len)
 diff_cmp(char_u *s1, char_u *s2)
 {
     char_u	*p1, *p2;
-#ifdef FEAT_MBYTE
     int		l;
-#endif
 
     if ((diff_flags & (DIFF_ICASE | DIFF_IWHITE)) == 0)
 	return STRCMP(s1, s2);
@@ -1983,10 +1981,8 @@ diff_find_change(
     int		idx;
     int		off;
     int		added = TRUE;
-#ifdef FEAT_MBYTE
     char_u	*p1, *p2;
     int		l;
-#endif
 
     /* Make a copy of the line, the next ml_get() will invalidate it. */
     line_org = vim_strsave(ml_get_buf(wp->w_buffer, lnum, FALSE));

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1056,
 /**/
     1055,
 /**/