Remove Date#getVarDate from scripthost lib

[Copilot]

lib.scripthost.d.ts declared Date#getVarDate, but that method is not present on real Date instances. Referencing scripthost incorrectly allowed calls like:

/// <reference lib="scripthost" />

new Date().getVarDate();

• Library surface

  • Removed getVarDate from the Script Host Date augmentation.

• Regression coverage

  • Added a compiler test that verifies Date#getVarDate is rejected even when scripthost is referenced.
  • Updated affected diagnostic baselines for the reduced Date member count.

• Fixes Date.getVarDate() function seems incorrectly defined #51636