Drop traprain test from target/hmi

The test case for traprain requires development and including gpgv to be
run, but installing them on target/hmi makes the test useless since it
does not resemble a standard target/hmi image. Drop it only run in on
sdk.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

test-cases/traprain.yaml

@@ -2,7 +2,6 @@ metadata:
   name: traprain
   format: "Apertis Test Definition 1.0"
   image-types:
-    target:  [ armhf, amd64 ]
     sdk:     [ amd64 ]
   image-deployment:
     - APT