patch 9.1.0923: too many strlen() calls in filepath.c

Problem:  too many strlen() calls in filepath.c
Solution: refactor filepath.c and remove calls to STRLEN(),
          unify dos_expandpath() and unix_expandpath() into
          a single function

closes: #16160

Signed-off-by: John Marriott <basilisk@internode.on.net>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/os_unix.c

@@ -6796,21 +6796,6 @@ select_eintr:
     return result;
 }
 
-/*
- * Expand a path into all matching files and/or directories.  Handles "*",
- * "?", "[a-z]", "**", etc.
- * "path" has backslashes before chars that are not to be expanded.
- * Returns the number of matches found.
- */
-    int
-mch_expandpath(
-    garray_T	*gap,
-    char_u	*path,
-    int		flags)		// EW_* flags
-{
-    return unix_expandpath(gap, path, 0, flags, FALSE);
-}
-
 /*
  * mch_expand_wildcards() - this code does wild-card pattern matching using
  * the shell