Revert "automake: complete the removal of the target package"

This reverts commit 6c33512e.

We DO need to look in the staging directory for .m4 files installed by other
target packages, otherwise we'll have breakage like:

http://autobuild.buildroot.net/results/b20/b20e3efcb0be3032781d7b2f0ef4c351834da0ce/



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>