[CI] remove obsolete workflow (#298)

Signed-off-by: Mikael Arguedas <mikael.arguedas@gmail.com>

.github/workflows/mirror-rolling-to-master.yaml

-name: Mirror rolling to master
-
-on:
-  push:
-    branches: [ rolling ]
-
-jobs:
-  mirror-to-master:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: zofrex/mirror-branch@v1
-      with:
-        target-branch: master