patch 9.0.1594: some internal error messages are translated

Problem:    Some internal error messages are translated.
Solution:   Consistently do not translate internal error messages.
            (closes #12459)
diff --git a/src/map.c b/src/map.c
index 4bdd07e..6020f63 100644
--- a/src/map.c
+++ b/src/map.c
@@ -2043,7 +2043,7 @@
 			c1 = 't';
 			break;
 		    default:
-			iemsg(_(e_makemap_illegal_mode));
+			iemsg(e_makemap_illegal_mode);
 			return FAIL;
 		}
 		do	// do this twice if c2 is set, 3 times with c3