Take out --allow-untyped-calls from mypy checks when drgn includes types to its helpers

[sdimitro]

There are currently failures that we'd hit hard if we enable this in the PR automation.
Some of them are related to drgn (missing stubs) but there are several other legitimate ones.

[sdimitro]

We've enabled --strict now with a09f135

Let's keep this open as a reminder to take out --allow-untyped-calls when drgn adds the rest of the types for its helper functions.

[sdimitro]

Closed by #246