Removal of Light UI

We are no longer building light ui as of 9.1.1 onwards
as agreed in @021-06-07 TSC+MDL+TF meeting:

- LW-UI failing 
  - Remove (@MarkB)
  - We will retag 9.1.1 as 9.1.2

Change-Id: I0f607dc076020727239017a9b6f428e6402b38d5
Signed-off-by: beierlm <mark.beierl@canonical.com>