update doc. remove #52 from known issue

doc/nvim-completion-manager.txt

@@ -772,20 +772,7 @@ to start it manually:
 ==============================================================================
 9. Known issues					*NCM-known-issues*
 
-9.1 Significant delay when exiting from vim8	*NCM-issue#52*
-
-There are two main causes:
-
-- The vim-hug-neovim-rpc uses multithread implementation. Vim has to wait for
-  all threads exit before shutdown, even though those are python daemon
-  thread.
-
-- The current version of NCM is runs outside of vim process and it is started
-  via the |job_start| function.  However, the |job_start| method provided by
-  vim8, unlike the |jobstart| in neovim, has no detach option available, which
-  means that vim8 has to wait for NCM process exit before shutdown.
-
-9.2 CTRL-L of |popupmenu-keys| is broken	*NCM-issue#127*
+9.1 CTRL-L of |popupmenu-keys| is broken	*NCM-issue#127*
 
 It seems this key is in-compatible with vim's |complete()| function.