[lib] Inline innerThreadFrozenDueToBlock in threadFrozenDueToBlock

Summary:
threadFrozenDueToBlock was last callsite of innerThreadFrozenDueToBlock, so inlining and removing innerThreadFrozenDueToBlock altogether.

Depends on D12292

Test Plan: flow + close reading

Reviewers: ashoat, ginsu, tomek, varun

Reviewed By: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12293