Remove filterdiff and use native git instead

Long ago, we needed the ability to filter out files and directories from patches. Now that ability is built into git a few years ago, let's use that instead of filterdiff.

One less tool to depend on and require.

Cc: Bastien Nocera bnocera@redhat.com Cc: Herton Krzesinski hkrzesin@redhat.com Signed-off-by: Don Zickus dzickus@redhat.com