Remove steps for unused linux-dev-yaml test builder

These steps were used while testing the transition to dynamic steps.
Now that dynamic steps are working properly, this builder has been
decommissioned, and its steps are no longer needed.

etc/ci/buildbot_steps.yml

@@ -54,18 +54,6 @@ linux-dev:
   - bash ./etc/ci/manifest_changed.sh
   - bash ./etc/ci/check_no_unwrap.sh
 
-linux-dev-yaml:
-  - ./mach test-tidy --no-progress --all
-  - ./mach test-tidy --no-progress --self-test
-  - ./mach build --dev
-  - ./mach test-compiletest
-  - ./mach test-unit
-  - ./mach build-cef
-  - ./mach build-geckolib
-  - bash ./etc/ci/lockfile_changed.sh
-  - bash ./etc/ci/manifest_changed.sh
-  - bash ./etc/ci/check_no_unwrap.sh
-
 linux-rel-wpt:
   - ./mach build --release
   - ./mach test-wpt-failure