Remove packages/platform from dependabot config

[jmagman]

Package was removed in #6898.

However the path was still being passed to dependabot, which made it mad:

ERROR <job_916983349> Error during file fetching; aborting: No files found in /packages/platform/example/android/app

https://github.com/flutter/packages/actions/runs/11845225387/job/33010210199

I don't understand why this only started failing on #8044 and not when the package was removed (since it moved that path from one place to another https://github.com/flutter/packages/pull/8036/files#diff-dd4fbda47e51f1e35defb9275a9cd9c212ecde0b870cba89ddaaae65c5f3cd28L571)

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[ditman]

LGTM! Landing on red to fix the tree!

[ditman]

I don't understand why this only started failing on #8044 and not when the package was removed

As @jmagman correctly suspects, this started failing earlier, but the errors went ignored. Here's an earlier failure:

• dcf47df ([flutter_svg] Initial import #7944)

And here's the dependabot failure:

• https://github.com/flutter/packages/actions/runs/11616982022/job/32351158495#step:3:38

🤖 ~ starting update ~
Fetching job details
...
updater | 2024/10/31 17:36:55 ERROR <job_909746212> Error during file fetching; aborting: No files found in /packages/platform/example/android/app
...
Dependabot encountered '1' error(s) during execution, please check the logs for more details.
+---------------------------+
|          Errors           |
+---------------------------+
| dependency_file_not_found |
+---------------------------+
Failure running container 7b087bcc3c8793d8403cb0765adc678a83f7a89e[47](https://github.com/flutter/packages/actions/runs/11616982022/job/32351158495#step:3:49)d2561867262766fb826ed0
...
For more information see: https://github.com/flutter/packages/network/updates/909746212 (write access to the repository is required to view the log)
🤖 ~ finished: error reported to Dependabot ~

Found it by sifting through this list of failed dependabot runs:

• https://github.com/flutter/packages/actions?query=event%3Adynamic+is%3Afailure