patch 8.0.0986: terminal feature always requires multi-byte feature

Problem:    Terminal feature always requires multi-byte feature.
Solution:   Remove #ifdef FEAT_MBYTE, disable terminal without multi-byte.
diff --git a/src/feature.h b/src/feature.h
index ae3859b..b7f3664 100644
--- a/src/feature.h
+++ b/src/feature.h
@@ -1269,8 +1269,10 @@
 
 /*
  * +terminal		":terminal" command.  Runs a terminal in a window.
+ *			requires +channel and +multibyte
  */
-#if !defined(FEAT_JOB_CHANNEL) && defined(FEAT_TERMINAL)
+#if defined(FEAT_TERMINAL) && \
+	!(defined(FEAT_JOB_CHANNEL) && defined(FEAT_MBYTE))
 # undef FEAT_TERMINAL
 #endif
 #if defined(FEAT_TERMINAL) && !defined(CURSOR_SHAPE)