UI/cleanup: Remove most redraw_later_clear() calls

Vim :! may "mess up the screen" because of e.g. switching between cooked
mode, but Nvim just uses pipes. So maybe we can avoid these
redraw_later_clear() CYA calls.

src/nvim/ex_cmds.c

@@ -1176,16 +1176,6 @@ static void do_filter(
   cmd_buf = make_filter_cmd(cmd, itmp, otmp);
   ui_cursor_goto((int)Rows - 1, 0);
 
-  /*
-   * When not redirecting the output the command can write anything to the
-   * screen. If 'shellredir' is equal to ">", screen may be messed up by
-   * stderr output of external command. Clear the screen later.
-   * If do_in is FALSE, this could be something like ":r !cat", which may
-   * also mess up the screen, clear it later.
-   */
-  if (!do_out || STRCMP(p_srr, ">") == 0 || !do_in)
-    redraw_later_clear();
-
   if (do_out) {
     if (u_save((linenr_T)(line2), (linenr_T)(line2 + 1)) == FAIL) {
       xfree(cmd_buf);

src/nvim/ex_docmd.c

@@ -6342,9 +6342,7 @@ static void ex_hide(exarg_T *eap)
     }
 }
 
-/*
+/// ":stop" and ":suspend": Suspend Vim.
- * ":stop" and ":suspend": Suspend Vim.
- */
 static void ex_stop(exarg_T *eap)
 {
   // Disallow suspending in restricted mode (-Z)
@@ -6363,7 +6361,6 @@ static void ex_stop(exarg_T *eap)
     ui_flush();
     maketitle();
     resettitle();  // force updating the title
-    redraw_later_clear();
     ui_refresh();  // may have resized window
     apply_autocmds(EVENT_VIMRESUME, NULL, NULL, false, NULL);
   }

src/nvim/os_unix.c

@@ -419,7 +419,6 @@ int mch_expand_wildcards(int num_pat, char_u **pat, int *num_file,
     xfree(tempname);
     // With interactive completion, the error message is not printed.
     if (!(flags & EW_SILENT)) {
-      redraw_later_clear();             // probably messed up screen
       msg_putchar('\n');                // clear bottom line quickly
 #if SIZEOF_LONG > SIZEOF_INT
       assert(Rows <= (long)INT_MAX + 1);

src/nvim/screen.c

@@ -158,10 +158,7 @@ void redraw_win_later(win_T *wp, int type)
   }
 }
 
-/*
+/// Forces a complete redraw later.  Also resets the highlighting.
- * Force a complete redraw later.  Also resets the highlighting.  To be used
- * after executing a shell command that messes up the screen.
- */
 void redraw_later_clear(void)
 {
   redraw_all_later(CLEAR);