[wpa] Remove PMKID checking

[wpa] Remove PMKID checking

PMKID checking is an additional pre-check that helps detect invalid
passphrases before going through the full handshaking procedure. It
takes up some amount of code size, and is not necessary from a
security perspective. It also is implemented improperly by some
routers, which was causing iPXE to give spurious authentication
errors. Remove it for these reasons.

Signed-off-by: Joshua Oreman <oremanj@rwcr.net>
Signed-off-by: Michael Brown <mcb30@ipxe.org>