redo-if{change,create}: print a useful message if REDO isn't set.

Again, I forgot to make vars.py not crash if the variables aren't set, so we
can print a useful error message.  But this time I have the right solution:
vars.py will do the checking for itself, and abort with a nice message.

redo-ifcreate.py

@@ -4,10 +4,6 @@ import vars, state
 from helpers import err, mkdirp
 
 
-if not vars.TARGET:
-    err('redo-ifcreate: error: must be run from inside a .do\n')
-    sys.exit(100)
-
 try:
     for t in sys.argv[1:]:
         if os.path.exists(t):