fix(@schematics/angular): remove browser field from generated angular.json

[cexbrayat]

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

The browser field is now optional with a default value of 'src/main.ts' as of commit c560d44.

What is the new behavior?

This remove the explicit browser field from the application schematic template since it's no longer needed.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[cexbrayat]

The private-e2e schematic fails for a reason unclear to me.
If you have an idea, I can take a look, otherwise feel free to close the PR if this is too complicated.

[alan-agius4]

The browser option value has been retained in the angular.json, as we need to ensure that all migrations can infer the value when not present.