Remove references to soon-to-be-deprecated "flutter create --ios-language" flag

[jmagman]

Page URLs

• https://docs.flutter.dev/platform-integration/platform-channels#example-project
• https://docs.flutter.dev/packages-and-plugins/developing-packages#step-1-create-the-package-1

There may be others.

Describe the problem

flutter create --ios-language (abbreiviated to -i) flag will be removed in a future release, and will default to Swift. Remove references to the flag in the website. It's referenced as -i swift and -i objc.

Expected fix

https://github.com/flutter/website/blob/d7787d061fa327c985c6ca2aef3f0ed3adefecac/src/content/platform-integration/platform-channels.md?plain=1#L267-L271 Remove the Objective-C part:

By default, our template supports writing Android code using Kotlin. To use Java, use the -a flag:

• In a terminal run: flutter create -a java batterylevel

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Also around here https://github.com/flutter/website/blob/d7787d061fa327c985c6ca2aef3f0ed3adefecac/src/content/packages-and-plugins/developing-packages.md?plain=1#L350 https://github.com/flutter/website/blob/d7787d061fa327c985c6ca2aef3f0ed3adefecac/src/content/packages-and-plugins/developing-packages.md?plain=1#L359-L364

Additional context

More context for the flag removal in https://github.com/flutter/flutter/issues/148586

I would like to fix this problem.

• [ ] I will try and fix this problem on docs.flutter.dev.