RTA is using different means to install Squish for RTA tests, no need
to do it in general provisioning.
Pick-to: 6.11
Change-Id: I4858a282ad7a0b1412f6dd0f4876109fe54a4c88
Reviewed-by: Tero Heikkinen <tero.heikkinen@qt.io>
Reviewed-by: Jukka Jokiniva <jukka.jokiniva@qt.io>