Fix template validation error

Commit 9c72ebccd3 introduced a bug: all template strings are validated against the disc template RegEx (which, for example, is wrong if we're testing the track template).

whipper/common/program.py

@@ -196,10 +196,6 @@ class Program:
         """
         assert isinstance(outdir, unicode), "%r is not unicode" % outdir
         assert isinstance(template, unicode), "%r is not unicode" % template
-        matches = re.findall(r"%[^A,S,d,y,r,R,x,X]", template)
-        if '%' in template and matches:
-            raise ValueError('disc template string contains invalid '
-                             'variable(s): {}.'.format(', '.join(matches)))
         v = {}
         v['A'] = 'Unknown Artist'
         v['d'] = mbdiscid  # fallback for title