Vcs: Use PagedSettings for all plugin settings

Hopefully the last structural change for a while.

Settings lifetime is again tied to the plugin private.

Change-Id: I221e8b8baa69422306191b48a9f034ef5b1a0dc2
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gitsettings.h

@@ -3,7 +3,6 @@
 
 #pragma once
 
-#include <coreplugin/dialogs/ioptionspage.h>
 #include <vcsbase/vcsbaseclientsettings.h>
 
 namespace Git::Internal {
@@ -48,10 +47,4 @@ public:
 
 GitSettings &settings();
 
-class GitSettingsPage final : public Core::IOptionsPage
-{
-public:
-    GitSettingsPage();
-};
-
 } // Git::Internal