Removing `load_plugin_textdomain` and leaving only `load_textdomain`.
This is standard as per new WordPress practices[0].
Ultimately, it makes language files more portable as they are still accessible via WordPress even if the plugin developer did not include them with the plugin itself.
Related #120
[0] d2eb67079b (commitcomment-4644357)
Signed-off-by: Tom McFarlin <tom@tommcfarlin.com>