Changes to the plugin.py file to include the plugin remove_jar feature

[nanaessuman]

I added "remove_jar" to plugin.jar to allow users to remove jars from directories when they add files with the add_jar feature.

[rschlussel-zz]

For remove jar, there is no local path. The command should take the plugin name to remove and optionally the remote path to the plugin directory to allow for non-default configurations.

def remove_jar(plugin_name, plugin_dir=REMOTE_PLUGIN_DIR)

[rschlussel-zz]

Thanks for the patch! We're excited to have a new contributor!
A couple notes on testing:
You should run 'make lint' to ensure that the code adheres to our style.
It's best to test with at least one presto node on a different node from presto-admin. Usually we write product tests to be able to run this automatically, but it's a bit complicated to set up, so it's fine if you just verify manually.

[kokosing]

@nanaessuman Could you please address the comments from @rschlussel ? So we could merge this PR.