build: fix pam library inclusion and usage

The pam_misc was deliberately included by the
Makefile_am, however, no calls into pam_ were made
from libuserlayer.  Pam calls were made from
usercommand.cpp, in libipmi20.so.  The calls are
part of the primary pam library.

Before:
objdump -t phosphor-host-ipmid/.libs/libipmi20.so\
 |grep "UND"|grep -v "@@"|grep "pam"
0000000000000000 *UND* 0000000000000000 pam_end
0000000000000000 *UND* 0000000000000000 pam_chauthtok
0000000000000000 *UND* 0000000000000000 pam_start

Now:
objdump -t ./.libs/libipmi20.so|grep "UND"|grep pam
0000000000000000 F *UND* 0000000000000000 pam_chauthtok@@LIBPAM_1.0
0000000000000000 F *UND* 0000000000000000 pam_end@@LIBPAM_1.0
0000000000000000 F *UND* 0000000000000000 pam_start@@LIBPAM_1.0

Tested: Searched objects for undefined pam calls
and found the information above.
Change-Id: I44aa570a2087affafba09886fbf17fa9d99abe05
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/Makefile.am b/Makefile.am
index c3535ba..e053550 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -78,7 +78,6 @@
 	$(PHOSPHOR_DBUS_INTERFACES_LIBS) \
 	-lstdc++fs \
 	$(CRYPTO_LIBS) \
-	-lpam_misc \
 	-version-info 0:0:0 -shared
 libuserlayer_la_CXXFLAGS = \
 	$(SYSTEMD_CFLAGS) \
@@ -126,6 +125,7 @@
 	$(libmapper_LIBS) \
 	$(PHOSPHOR_LOGGING_LIBS) \
 	$(PHOSPHOR_DBUS_INTERFACES_LIBS) \
+	$(LIBS) \
 	-lstdc++fs \
 	-luserlayer \
 	-version-info 0:0:0 -shared