Git: Make Gerrit settings handling more similar to others

Use a singleton for the main settings, don't pass it around as
shared pointer.

Change-Id: I5c32679452ad631998a688afc9a6e2b154bf3a5d
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/git/gerrit/gerritplugin.h

@@ -17,12 +17,10 @@ class CommandLocator;
 
 namespace VcsBase { class VcsBasePluginState; }
 
-namespace Gerrit {
-namespace Internal {
+namespace Gerrit::Internal {
 
 class GerritChange;
 class GerritDialog;
-class GerritParameters;
 class GerritServer;
 class GerritOptionsPage;
 
@@ -54,7 +52,6 @@ private:
     Utils::FilePath findLocalRepository(const QString &project, const QString &branch) const;
     void fetch(const std::shared_ptr<GerritChange> &change, int mode);
 
-    std::shared_ptr<GerritParameters> m_parameters;
     std::shared_ptr<GerritServer> m_server;
     QPointer<GerritDialog> m_dialog;
     Core::Command *m_gerritCommand = nullptr;
@@ -63,5 +60,4 @@ private:
     GerritOptionsPage *m_gerritOptionsPage = nullptr;
 };
 
-} // namespace Internal
-} // namespace Gerrit
+} // Gerrit::Internal