drm/vkms: Remove useless call to drm_connector_register/unregister()

The function vkms_output_init() is invoked during the module
initialization, and it handles the creation/configuration of the vkms
essential elements (e.g., connectors, encoder, etc). Among the
initializations, this function tries to initialize a connector and
register it by calling drm_connector_register(). However, inside the
drm_connector_register(), at the beginning of this function there is the
following validation:

 if (!connector->dev->registered)
   return 0;

In this sense, invoke drm_connector_register() after initializing the
connector has no effect because the register field is false. The
connector register happens when drm_dev_register() is invoked; the same
issue exists with drm_connector_unregister(). Therefore, this commit
removes the unnecessary call to drm_connector_register() and
drm_connector_unregister().

Changes since v2:
* Remove unnecessary call to drm_connector_unregister()
* Remove unused label

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Reviewed-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20190315161142.23gfu32lueyqrmyq@smtp.gmail.com