contrib/wpa: Complete the revert of Import wpa.

Remove files added by b51f459a2098622c31ed54f5c1bf0e03efce403b.
The util/config.c conflicts with wpa_supplicant/config.c causing
the linker error.

The proper approach would have been to prepare the wpa build to
build the various subdirectories into .a libraries. SRCS makes no
distinction between files of the same name. The MFV accounted for this
but the revert failed to remove the additional files, including the
conflicting utils/config.c.