Commit f21b2558a097 (busybox: added linux-pam support, 2015-06-02) added
linux-pam support already, no need to do this again. Commit 083aeac94e19
(busybox: added linux-pam support, 2015-07-14) also effectively annulled the
build failure fix from commit 98e1848db11e (busybox: PAM support needs thread
support, 2015-07-04). Revert it.