Apply 'static' pattern to VcsManager

Adapt user and surrounding code.

Change-Id: Id2648f82a9cbbd0ad0bfb91f6958b8cee7ea29cc
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/coreplugin/icore.cpp

@@ -349,11 +349,6 @@ bool ICore::showWarningWithOptions(const QString &title, const QString &text,
                                                 settingsId, parent);
 }
 
-VcsManager *ICore::vcsManager()
-{
-    return m_mainwindow->vcsManager();
-}
-
 QSettings *ICore::settings(QSettings::Scope scope)
 {
     return m_mainwindow->settings(scope);