gnu: emacs-magit: Update to commit d05545e.

* gnu/packages/emacs-xyz.scm (emacs-magit): Update to commit
68b5a13fa1b6b122d4a2547b8c415aadff83d8ca.
[origin]: Remove obsoleted patches and snippets.
[build-system]: Switch to the emacs-build-system.
[arguments]: Remove the #:modules and #:imported-modules arguments.  Enable
tests. Remove the #:make-flags and #:test-target argument.  Specify the
\#:test-command argument.
[phases]{patch}: Remove phase.
{build-info-manual, set-magit-version, configure-git}
{disable-tramp-test}: New phases.
{configure}: Do not delete phase.
{patch-exec-paths}: Adapt file names.
* gnu/packages/patches/emacs-magit-log-format-author-margin.patch: Remove file.
* gnu/local.mk (dist_patch_DATA): Unregister it.