[web] Rename usernameOrEmail to username in LogInModal
[web] Rename usernameOrEmail to username in LogInModal

Summary: I removed the email logic in D1441 but forgot to rename the property.

Test Plan: Flow

Reviewers: atul, palys-swm

Reviewed By: palys-swm

Subscribers: KatPo, Adrian

Differential Revision: https://phabricator.ashoat.com/D1483

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