Fix package update from local repository mirror.

Fix package update from local repository mirror.

	When updating packages from a local repository, package-get would
	attempt to remove the file.
	While this is useful behaviour for files downloaded from an update
	site, for local directories it is not a good thing ;)

	* lisp/package-get.el (package-get): move host to the uppermost
	let. Surround all (delete-file full-package-filename) with (unless
	(null host)

Signed-off-by: Nelson Ferreira <nelson.ferreira@ieee.org>