correctly clean up post command hooks (#4550)

Co-authored-by: sam <[email protected]>

Author: sstraust

lsp-mode.el

@@ -4122,7 +4122,8 @@ yet."
     (cond
      ((and (or (equal lsp-signature-auto-activate t)
                (memq :on-trigger-char lsp-signature-auto-activate))
-           signature-help-handler)
+           signature-help-handler
+           (not cleanup?))
       (add-hook 'post-self-insert-hook signature-help-handler nil t))
 
      ((or cleanup?