Remove pyrightconfig.json file as it doesn't belong here

This is a VSCode specific json file. Better to put the setting directly
into VSCode. Also if you're using Pylance, this already includes Pyright
so you don't need to add settings for Pyright specifically.

Note: There are some performance improvements and semantic differences
over mypy. See disccusion here [1] and [2].

"python.analysis.diagnosticSeverityOverrides": {
    "reportUndefinedVariable": "none",
    "reportGeneralTypeIssues": "none",
    "reportIncompatibleMethodOverride": "error",
    "reportMissingParameterType": "error",
    "reportMissingTypeStubs": "error",
    "typeCheckingMode": "basic",
    "venv": ".venv",
    "venvPath": "."
},

The setting "python.analysis.diagnosticSeverityOverrides" in .vscode is
specific to Pylance, the default language server for Python in Visual
Studio Code.

[1] https://news.ycombinator.com/item?id=34222407
[2] https://github.com/microsoft/pyright/blob/main/docs/mypy-comparison.md