Remove dx/tests/120-disable-extend-ops

Support for the target-api flag was removed in 2011.

Change-Id: Id50c53f759d4e3a59f550dbeb6e733b68df58dd3
Remove code related to extended-opcode.

- This support was removed one year ago.

(cherry-pick from commit 18b65cbb3ec6634618bd3240a692507432e634b5)

Change-Id: I1154e518dc8a15220f2fcb163056570030492bb0