nvim: Fix loading of git messenger

Relying on lazy loading on command invocation feature seems to not make the
default key bindings of the plugin take effect. Remove it.

nvim/.config/nvim/lua/plugins.lua

@@ -47,10 +47,7 @@ local init = function ()
     branch = 'main'
   }
   use 'lambdalisue/gina.vim'
-  use {
-    'rhysd/git-messenger.vim',
-    cmd = 'GitMessenger'
-  }
+  use 'rhysd/git-messenger.vim'
   use 'rhysd/conflict-marker.vim'
   use 'salcode/vim-interactive-rebase-reverse'
   -- Boost vim command line mode