Remove useless NULL casts from mv(1)

[Michael McConville]

Index: mv.c
===================================================================
RCS file: /cvs/src/bin/mv/mv.c,v
retrieving revision 1.40
diff -u -p -r1.40 mv.c
--- mv.c        24 Aug 2015 00:10:59 -0000      1.40
+++ mv.c        14 Sep 2015 13:38:13 -0000
@@ -348,7 +348,7 @@ copy(char *from, char *to)
        pid_t pid;
 
        if ((pid = vfork()) == 0) {
-               execl(_PATH_CP, "cp", "-PRp", "--", from, to, (char *)NULL);
+               execl(_PATH_CP, "cp", "-PRp", "--", from, to, NULL);
                warn("%s", _PATH_CP);
                _exit(1);
        }
@@ -366,7 +366,7 @@ copy(char *from, char *to)
                return (1);
        }
        if (!(pid = vfork())) {
-               execl(_PATH_RM, "cp", "-rf", "--", from, (char *)NULL);
+               execl(_PATH_RM, "cp", "-rf", "--", from, NULL);
                warn("%s", _PATH_RM);
                _exit(1);
        }