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/feature.h b/src/feature.h
index 6334288..26296d3 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -127,6 +127,8 @@
  *			Support was removed in 8.1.1093.
  * +farsi		Farsi (Persian language) Keymap support.
  *			Removed in patch 8.1.0932
+ * +footer		Motif only: Add a message area at the bottom of the
+ *			main window area.
  */
 
 /*
@@ -1133,14 +1135,6 @@
 # endif
 #endif
 
-#if 0
-/*
- * +footer		Motif only: Add a message area at the bottom of the
- *			main window area.
- */
-# define FEAT_FOOTER
-#endif
-
 /*
  * +autochdir		'autochdir' option.
  */