Remove global pythonPath setting

Just depend on setting it in each project.

Setting python.venvPath and/or python.venvFolders doesn't seem to work,
and vscode doesn't support Poetry environments natively yet.

The interpreter discovery in vscode is being refactored:
microsoft/vscode-python#12020

Revisit when that's done.

HOME/Library/Application Support/Code/User/settings.json

@@ -216,7 +216,6 @@
             "source.organizeImports": true
         }
     },
-    "python.pythonPath": "/Users/kbd/.pyenv/shims/python3",
     "python.formatting.provider": "black",
     "python.sortImports.args": ["-m3", "--tc", "--ca"],
     "python.testing.pytestEnabled": true,