patch 9.0.0375: the footer feature is unused

Problem:    The footer feature is unused.
Solution:   Remove FEAT_FOOTER and code.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 7c122e1..2c041fa 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -5650,13 +5650,7 @@
 		0
 #endif
 		},
-	{"footer",
-#ifdef FEAT_FOOTER
-		1
-#else
-		0
-#endif
-		},
+	{"footer", 0},
 	{"fork",
 #if !defined(USE_SYSTEM) && defined(UNIX)
 		1