libpam: be more script about user's sanity

* replace do_pam_sanity function with distro_features_check inherit
* fixes:
WARNING: libpam-1.3.0-r5 do_pam_sanity: Building libpam but 'pam' isn't in DISTRO_FEATURES, PAM won't work correctly in world builds and prevents user to build libpam at all without pam
in DISTRO_FEATURES, I don't see any users of this which wouldn't respect
pam in DISTRO_FEATURES
* only libuser is depending on libpam without respecting DISTRO_FEATURES
* there are few recipes in meta-oe layers depending on libpam without
respecting DISTRO_FEATURES, I've sent patch for them:
samba, openwsman, pam-ssh-agent-auth, sblim-sfcb, passwdqc, python-pam, smbnetfs
and omxplayer in meta-raspberrypi, I've sent PR for that one:
https://github.com/agherzan/meta-raspberrypi/pull/192

---
 meta/recipes-extended/libuser/libuser_0.62.bb | 3 +++
 meta/recipes-extended/pam/libpam_1.3.0.bb     | 7 ++-----
 2 files changed, 5 insertions(+), 5 deletions(-)

index 1765346646..7ec54eb16e 100644
@@ -22,6 +22,9 @@ SRC_URI[sha256sum] = "a58ff4fabb01a25043b142185a33eeea961109dd60d4b40b6a9df4fa3c
 
 DEPENDS = "popt libpam glib-2.0 python3"
 
+inherit distro_features_check
+REQUIRED_DISTRO_FEATURES = "pam"
+
 inherit autotools gettext python3native python3-dir pkgconfig gtk-doc
 
 EXTRA_OEMAKE = "PYTHON_CPPFLAGS=-I${STAGING_INCDIR}/${PYTHON_DIR}${PYTHON_ABI}"

index 8f7753d001..92ab72a42f 100644
@@ -151,11 +151,8 @@ do_install() {
 	fi
 }
 
-python do_pam_sanity () {
-    if not bb.utils.contains('DISTRO_FEATURES', 'pam', True, False, d):
-        bb.warn("Building libpam but 'pam' isn't in DISTRO_FEATURES, PAM won't work correctly")
-}
-addtask pam_sanity before do_configure
+inherit distro_features_check
+REQUIRED_DISTRO_FEATURES = "pam"
 
 BBCLASSEXTEND = "nativesdk native"
 

2.15.1