patch 9.1.1757: The colorresp plugin causes additional redraws

Problem:  The colorresp plugin causes additional redraws
          (Linwei, after v9.1.1703)
Solution: Move the code back into the C core and get rid of the vim
          plugin (Foxe Chen)

fixes: #18251
closes: #18279

Signed-off-by: Foxe Chen <chen.foxe@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/main.c

@@ -883,6 +883,8 @@ vim_main2(void)
     // Requesting the termresponse is postponed until here, so that a "-c q"
     // argument doesn't make it appear in the shell Vim was started from.
     may_req_termresponse();
+
+    may_req_bg_color();
 #endif
 
     // start in insert mode