gen_licenses.py: Strip __download suffix from JS libs

In our build rules we have a convention of appending suffixes with __
to indicate an internal implementation detail of one of our custom
macros. Now that the download rules for bower_component rules end in
__download, this is slightly unsightly in licenses.txt. Fix this by
stripping any __ suffix in gen_licenses.py.

Change-Id: Ibea2b03cac26175b034e82ca2a94631ff2863701

Documentation/gen_licenses.py

@@ -166,6 +166,8 @@ for n in used:
       p = d[len('//lib:'):]
     else:
       p = d[d.index(':')+1:].lower()
+    if '__' in p:
+      p = p[:p.index('__')]
     print('* ' + p)
   if args.asciidoc:
     print()