[gdm] Revert "configure: require plymouth if using systemd"

[Ray Strode <halfline src gnome org>]

commit a3ebb3ed46b89b10e075061bfdd5da130f4f9d10
Author: Ray Strode <rstrode redhat com>
Date:   Fri Dec 19 08:49:47 2014 -0500

    Revert "configure: require plymouth if using systemd"
    
    This reverts commit f8a21cd6cb2095e80889df8c41036e2df31ba01a.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=740802

 configure.ac |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index f9b1d35..a567a82 100644
--- a/configure.ac
+++ b/configure.ac
@@ -972,7 +972,7 @@ PKG_CHECK_MODULES(PLYMOUTH,
 
 if test "x$with_plymouth" = "xauto" ; then
         if test x$have_plymouth = xno ; then
-                use_plymouth=$use_systemd
+                use_plymouth=no
         else
                 use_plymouth=yes
         fi
@@ -982,7 +982,7 @@ fi
 
 if test "x$use_plymouth" != "xno" ; then
         if test "x$have_plymouth" = "xno"; then
-                AC_MSG_ERROR([Plymouth support required, but plymouth not found])
+                AC_MSG_ERROR([Plymouth support explicitly required, but plymouth not found])
         fi
 
         AC_DEFINE(WITH_PLYMOUTH, 1, [Define to enable plymouth support])