Upstream vendored dev-python/ply, but we can keep using the one in ::gentoo

--- a/setup.py
+++ b/setup.py
@@ -20,8 +20,6 @@
     },
     packages=[
         'stone',
-        'stone._vendor',
-        'stone._vendor.ply',
         'stone.backends',
         'stone.backends.python_rsrc',
         'stone.frontend',
@@ -29,7 +27,6 @@
     ],
     package_data={
         'stone': ['py.typed'],
-        'stone._vendor.ply': ['LICENSE', 'README.md'],
     },
     zip_safe=False,
     author_email='kelkabany@dropbox.com',
--- a/stone/cli_helpers.py
+++ b/stone/cli_helpers.py
@@ -1,6 +1,6 @@
 import abc
 
-from stone._vendor.ply import lex, yacc
+from ply import lex, yacc
 
 _MYPY = False
 if _MYPY:
--- a/stone/frontend/lexer.py
+++ b/stone/frontend/lexer.py
@@ -1,7 +1,7 @@
 import logging
 import os
 
-from stone._vendor.ply import lex
+from ply import lex
 
 _MYPY = False
 if _MYPY:
--- a/stone/frontend/parser.py
+++ b/stone/frontend/parser.py
@@ -1,7 +1,7 @@
 import logging
 from collections import OrderedDict
 
-from stone._vendor.ply import yacc
+from ply import yacc
 
 from .ast import (
     AstAlias,