steam: Use /.local/share/Steam as install dir

In some cases, symlinks in /.steam can be broken in Flatpak, leading to no
games being detected. /.local/share/Steam seems to be more reliable.
6 jobs for wip/exalm/steam in 23 minutes and 15 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #203764
flatpak:app

00:09:07

 
  Test
passed #203765
flatpak:tests

00:03:26

 
  Review
passed #203766
review

00:00:22

passed #203767
manual
stop_review

00:00:28

 
  Cross Distro
passed #203768
fedora:29

00:03:10

passed #203769
ubuntu:devel

00:09:49