OS X: Don't add libtool control files to the app bundle.

According to https://developer.apple.com/library/mac/technotes/tn2206
the Contents/PlugIns directory should *only* contain executable files.
Only copy .so (and in case we need them) .dylib files.

Change-Id: I01f077735018733926db92e7576f6f4fecb68862
Reviewed-on: https://code.wireshark.org/review/5008
Reviewed-by: Gerald Combs <gerald@wireshark.org>