Disable call signature hints if auto_initialization is off

I recently changed my completions setup (again...) to use `omnifunc=jedi#complete` directly. I have mappings etc. already so I promptly set:
```
let g:jedi#auto_initialization = 0
let g:jedi#auto_vim_configuration = 0
```
in my vimrc, which mostly worked as expected. However, I still got call signature hints, which weren't cleared after exiting insert mode. From `:h g:jedi#show_call_signatures`:
```
Note: This setting is ignored if |g:jedi#auto_initialization| is set to 0. In
that case, if you want to see call signatures, you have to set it up
manually by calling a function in your configuration file: >
```
In other words, the autocommand block in `jedi#configure_call_signatures()` is not run, however the call signatures option is still enabled:
```
'show_call_signatures': has('conceal') ? 1 : 2
```
This results in broken call signature hints. Would it be possible to disable call signature hints if auto_initialization is off? I guess this is sort of mentioned in `:h g:jedi#auto_initialization` as one of the functions it performs:
```
3. Call `jedi#configure_call_signatures()` if
`g:jedi#show_call_signatures` is set
```
but it doesn't explicitly warn that show_callsignatures will not be turned off.

Just a little suggestion for QoL improvement. Thanks for jedi! :)