Switch to using gettext:compile instead of gettext:pack in the install

Docs

This skips the step that updates the .pot files with changes in the
codebase, which can take extra time, and isn't required during install.

doc/install/installation.md

@@ -513,8 +513,7 @@ Check if GitLab and its environment are configured correctly:
 ### Compile GetText PO files
-    sudo -u git -H bundle exec rake gettext:pack RAILS_ENV=production
-    sudo -u git -H bundle exec rake gettext:po_to_json RAILS_ENV=production
+    sudo -u git -H bundle exec rake gettext:compile RAILS_ENV=production
 ### Compile Assets