Remove all the examples' podfiles

[xster]

So the podfile template can be exercised instead of checking in stale ones

[mravn-google]

I think we need to update relevant .gitignore file(s) to ignore the generated Podfiles. Otherwise, git clone + run example app will leave a dirty workspace.

While we're at it, we may want to make sure that the new Flutter/flutter_assets folder is ignored in iOS example projects, e.g. here.

[xster]

Did flutter assets in a separate PR #350

The Podfiles are a bit inconvenient but I'd argue it's the 'right' behaviour to have the workspace be in a dirty state after running building an example. If you want share the example with other people, the Podfile needs to be 'materialized' so everyone's builds are consistent.

[mravn-google]

The regular project templates surely do not gitignore the Podfiles. But for the template instantiations checked into our own repos, we've taken the approach so far to set them up to be clean after flutter run. The Gradle wrapper executables for instance are in gitignore for this reason.

[xster]

Ah I see. Makes sense to keep in sync with gradle wrappers. Done

[mravn-google]

Thanks. I think we can merge this now?

[Hixie]

@xster is this ready to land?

[xster]

My bad, I thought I already merged it.