Remove libdragon build in CI (it is already performed in devcontainer) (#35)

<!--- Provide a general summary of your changes in the Title above -->

## Description
<!--- Describe your changes in detail -->
The CI uses the devcontainer to build libdragon, but that has already
occured as part of the devcontainer initialization.

## Motivation and Context
<!--- What does this sample do? What problem does it solve? -->
<!--- If it fixes/closes/resolves an open issue, please link to the
issue here -->
The CI was taking longer to build than expected.

If/when we move to native CI, we should leverage the CI which would
include:

```
      # - name: Cache libDragon build
      #   id: cache-libdragon
      #   uses: actions/cache@v3
      #   env:
      #     cache-name: cache-libdragon
      #   with:
      #     # libdragon cache files are stored in `./libdragon`
      #     path: ./libdragon
      #     key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('./.gitmodules') }}
      #     restore-keys: |
      #       ${{ runner.os }}-build-${{ env.cache-name }}-
      #       ${{ runner.os }}-build-
      #       ${{ runner.os }}-

      # - name: Build libDragon
      #   if: ${{ steps.cache-libdragon.outputs.cache-hit != 'true' }}
      #   uses: devcontainers/ci@v0.3
      #   with:
      #     imageName: ghcr.io/polprzewodnikowy/n64flashcartmenu-devcontainer
      #     cacheFrom: ghcr.io/polprzewodnikowy/n64flashcartmenu-devcontainer
      #     push: ${{ github.repository_owner == 'Polprzewodnikowy' && 'filter' || 'never' }}
      #     refFilterForPush: refs/heads/main
      #     runCmd: |
      #        pushd libdragon
      #          ./build.sh
      #        popd
```

## How Has This Been Tested?
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to -->
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## Screenshots
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## Types of changes
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the boxes that apply: -->
- [ ] Improvement (non-breaking change that adds a new feature)
- [ ] Bug fix (fixes an issue)
- [ ] Breaking change (breaking change)
- [ ] Config and build (change in the configuration and build system,
has no impact on code or features)

## Checklist:
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that apply. -->
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here to help! -->
- [ ] My code follows the code style of this project.
- [ ] My change requires a change to the documentation.
- [ ] I have updated the documentation accordingly.
- [ ] I have added tests to cover my changes.
- [ ] All new and existing tests passed.

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replacing the name with your GitHub user name and GitHub email contact.
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Signed-off-by: GITHUB_USER <GITHUB_USER_EMAIL>

.github/workflows/build.yml

@@ -32,9 +32,6 @@ jobs:
           push: ${{ github.repository_owner == 'Polprzewodnikowy' && 'filter' || 'never' }}
           refFilterForPush: refs/heads/main
           runCmd: |
-            pushd libdragon
-            ./build.sh
-            popd
             make all -j
         env:
           FLAGS: -DMENU_RELEASE