if a build did verify against Binaries:, delete the comparison dirs

If the comparison between the provided APK and the built APK is verified,
then there is no need to keep the old comparison files around. On big build
servers like f-droid.org, there will be thousands of leftover dirs from all
the builds, so this is necessary.

fdroidserver/common.py

@@ -1918,6 +1918,10 @@ def compare_apks(apk1, apk2, tmp_dir):
             p = FDroidPopen(['meld', apk1dir, apk2dir], output=False)
         return("Unexpected diff output - " + p.output)
 
+    # since everything verifies, delete the comparison to keep cruft down
+    shutil.rmtree(apk1dir)
+    shutil.rmtree(apk2dir)
+
     # If we get here, it seems like they're the same!
     return None