Fix garbled output from Ctrl+Alt+V (#135)

This fixes a regression introduced in commit f9c127e3.
When the legacy code for older versions of libast was
removed, the fmtident wrapper wasn't removed. As a result,
the version string output by Ctrl+Alt+V is garbled because
the fmtident wrapper doesn't do any formatting:

$ <Ctrl+Alt+V>
^J@(#)$Id: Version AJM 93u+m 2020-09-14

src/cmd/ksh93/sh/string.c:
- Remove the old version of fmtident that was overriding
  the current version of fmtident provided by libast
  (in src/lib/libast/string/fmtident.c).

src/cmd/ksh93/sh/string.c

@@ -741,8 +741,3 @@ char *sh_checkid(char *str, char *last)
 	}
 	return(last);
 }
-
-char *fmtident(const char *string)
-{
-	return((char*)string);
-}