#276: Poetry: Fix missing reference to Silkaj entry point

Fixes #276 (closed):

• Add a Poetry scripts definition to Silkaj entry point: which generate the $HOME/.local/bin/silkaj executable.
• Clean now useless bin/silkaj and its references.

bin/silkaj

-#!/usr/bin/env python3
-
-"""
-Copyright  2016-2020 Maël Azimi <m.a@moul.re>
-
-Silkaj is free software: you can redistribute it and/or modify
-it under the terms of the GNU Affero General Public License as published by
-the Free Software Foundation, either version 3 of the License, or
-(at your option) any later version.
-
-Silkaj is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-GNU Affero General Public License for more details.
-
-You should have received a copy of the GNU Affero General Public License
-along with Silkaj. If not, see <https://www.gnu.org/licenses/>.
-"""
-
-from silkaj.cli import cli
-
-if __name__ == "__main__":
-    cli(obj={})