[RN0.66] 34/n: Hide type error in multer use

Summary:
This type error was caught as part of the Flow upgrade.

Express middleware are impossible to try correctly. We have to use a (carefully placed) any-type for this to typecheck.

Test Plan: Flow

Reviewers: palys-swm, atul, varun

Reviewed By: palys-swm

Subscribers: benschac, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3014