configure.in: edit message checking for new GStreamer 1.0

to not duplicate the message checking for old one
and be consistent with the help message in AS_HELP_STRING

Change-Id: I91e0a5ed0e2278de013d7872eadc6f93b970c231
Reviewed-on: https://gerrit.libreoffice.org/722Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>

configure.in

@@ -9519,7 +9519,7 @@ ENABLE_GSTREAMER=""
 
 if test "$build_gstreamer" = "yes"; then
 
-    AC_MSG_CHECKING([whether to enable the GStreamer avmedia backend])
+    AC_MSG_CHECKING([whether to enable the new GStreamer 1.0 avmedia backend])
     if test "x$enable_gstreamer" != "xno"; then
         ENABLE_GSTREAMER="TRUE"
         AC_MSG_RESULT([yes])