[web] Remove launch app button from Header at lower breakpoints

Summary: Remove the launch app button from Header below max-width of 1099px (where we go from the two-column to single-column layout).

Test Plan:
Looks as expected:

Reviewers: def-au1t, palys-swm, varun, benschac, ashoat

Reviewed By: ashoat

Subscribers: ashoat, Adrian, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D3478