github actions: remove package_updates.yml (automatic updates)

Begin phasing out dl.bintray.com/termux/termux-packages-24.

Before Bintray will go read-only (28 Feb), we need to ensure that
its repo has consistent state and no/minimal amount of issues as
large amount of users will continue to use it until Bintray finally
go down.

I still leaving autobuild/autodeploy (packages.yml) to Bintray repo
to process all remaining updates or pull requests with for short time.

.github/workflows/package_updates.yml

@@ -1,26 +0,0 @@
-name: Package updates
-
-on:
-  schedule:
-    - cron:  '0 */6 * * *'
-  workflow_dispatch:
-
-jobs:
-  update-packages:
-    runs-on: ubuntu-latest
-    steps:
-    - name: Clone repository
-      uses: actions/checkout@v2
-      with:
-        fetch-depth: 0
-        token: ${{ secrets.GH_API_KEY }}
-    - name: Process package updates
-      env:
-        GITHUB_API_TOKEN: ${{ secrets.GH_API_KEY }}
-        BUILD_PACKAGES: "true"
-        GIT_COMMIT_PACKAGES: "true"
-        GIT_PUSH_PACKAGES: "true"
-      run: |
-        git config --global user.name "Termux Github Actions"
-        git config --global user.email "leonid.pliushch@gmail.com"
-        bash ./scripts/updates/check-updates.sh