patch 8.0.1338: USE_IM_CONTROL is confusing and incomplete

Problem:    USE_IM_CONTROL is confusing and incomplete.
Solution:   Just use FEAT_MBYTE.  Call 'imactivatefunc' also without GUI.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index f8a193d..02d03b4 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -359,11 +359,11 @@
 	    b_im_ptr = &curbuf->b_p_imsearch;
 	if (*b_im_ptr == B_IMODE_LMAP)
 	    State |= LANGMAP;
-#ifdef USE_IM_CONTROL
+#ifdef FEAT_MBYTE
 	im_set_active(*b_im_ptr == B_IMODE_IM);
 #endif
     }
-#ifdef USE_IM_CONTROL
+#ifdef FEAT_MBYTE
     else if (p_imcmdline)
 	im_set_active(TRUE);
 #endif
@@ -1119,7 +1119,7 @@
 		{
 		    /* ":lmap" mappings exists, toggle use of mappings. */
 		    State ^= LANGMAP;
-#ifdef USE_IM_CONTROL
+#ifdef FEAT_MBYTE
 		    im_set_active(FALSE);	/* Disable input method */
 #endif
 		    if (b_im_ptr != NULL)
@@ -1130,7 +1130,7 @@
 			    *b_im_ptr = B_IMODE_NONE;
 		    }
 		}
-#ifdef USE_IM_CONTROL
+#ifdef FEAT_MBYTE
 		else
 		{
 		    /* There are no ":lmap" mappings, toggle IM.  When
@@ -2143,7 +2143,7 @@
 #endif
 
     State = save_State;
-#ifdef USE_IM_CONTROL
+#ifdef FEAT_MBYTE
     if (b_im_ptr != NULL && *b_im_ptr != B_IMODE_LMAP)
 	im_save_status(b_im_ptr);
     im_set_active(FALSE);