patch 8.1.0904: USE_LONG_FNAME never defined

Problem:    USE_LONG_FNAME never defined.
Solution:   Remove using USE_LONG_FNAME. (Ken Takata, closes #3938)
diff --git a/src/version.c b/src/version.c
index a6101b5..20fdcba 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    904,
+/**/
     903,
 /**/
     902,