params: Don't use Lang module

To copy the passed in default parameters, we can just as well use
another Object.assign() call.

GNOME/gnome-shell!616
4 jobs for !616 with params-cleanup in 5 minutes and 11 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Review
passed #350790
check_commit_log

00:00:21

 
  Build
passed #350791
build

00:03:50

 
  Test
passed #350792
test

00:00:56

passed #350793
test-pot

00:00:58