Remove redundant _config.yml quotes

BS3 commits: c7984d41ca967d600246d5729dd0b88c40a9650c
Fixes 12966: Ensure icon font vars are loaded into Customizer

BS3 commits: 03701b8d4bdda30dc625cdd263ca586835f544e3
grunt

BS3 commits: 67c747a109fb26b27bc255dd267c5262e51d5dcf,
bcfb27b962556a528579d742a60762831ed0c0ba