[web] Removed extraneous .loading-indicator-loading CSS selector

Summary: Noticed this CSS selector and rule was repeated twice in the same file. Removed the second occurrence.

Test Plan: Close reading.

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: ashoat, palys-swm, Adrian, karol-bisztyga, benschac

Differential Revision: https://phabricator.ashoat.com/D3606