Delegate FIPS mode detection to configured crypto backend.

System FIPS mode check is no longer dependent on /etc/system-fips
file. The change should be compatible with older distributions since
we now depend on crypto backend internal routine.

This commit affects only FIPS enabled systems (with FIPS enabled
builds). In case this causes any regression in current distributions
feel free to drop the patch.

For reference see https://bugzilla.redhat.com/show_bug.cgi?id=2080516

lib/crypto_backend/crypto_nss.c

@@ -400,3 +400,8 @@ int crypt_backend_memeq(const void *m1, const void *m2, size_t n)
 {
 	return NSS_SecureMemcmp(m1, m2, n);
 }
+
+bool crypt_fips_mode(void)
+{
+	return false;
+}