Macro cleanup: Miscellaneous

These were found with -Wunused-macros. There are many more macros which
triggered that warning, but they were primarily part of larger sets of
macros so leave them alone.

src/nvim/message.c

@@ -10,8 +10,6 @@
  * message.c: functions for displaying messages on the command line
  */
 
-#define MESSAGE_FILE            /* don't include prototype for smsg() */
-
 #include <assert.h>
 #include <errno.h>
 #include <inttypes.h>