state.py: remove all the ugly fromdir= stuff.

Instead, just change the target name to be more specific, in the one place
in redo-ifchange that actually needed it.

helpers.py

@@ -67,18 +67,3 @@ def debug2(s):
         log_('redo: %s%s' % (vars.DEPTH, s))
 
 
-def relpath(t, base):
-    t = os.path.abspath(t)
-    tparts = t.split('/')
-    bparts = base.split('/')
-    for tp,bp in zip(tparts,bparts):
-        if tp != bp:
-            break
-        tparts.pop(0)
-        bparts.pop(0)
-    while bparts:
-        tparts.insert(0, '..')
-        bparts.pop(0)
-    return '/'.join(tparts)
-
-