[native] Rename promises to cleanupPromises at end of uploadFile(...)

Summary:
There are a lot of promises in uploadFile(...)... figured giving this "section" of them a more descriptive name.

Depends on D4980

Test Plan: NA, simple rename

Reviewers: abosh, jacek, tomek, ashoat

Reviewed By: abosh

Differential Revision: https://phab.comm.dev/D4981