Remove the legacy bifrost jobs from the zuul jobs
repository as they should now be in-tree as a result
of Ic51078addb9282f777689fd769fa3507a29f2990.
Depends-On: I927f781caa18814e02845dcaeffe83ef965c4c39
Change-Id: I73c0ec019c204be2e0e87ab50411f05a325a3e75