These changes replace most usages of `removeChild` with `remove`. The latter has the advantage of not having to look up the `parentNode` and ensure that the child being removed actually belongs to the specific parent.
The refactor should be fairly safe since all the browsers we cover support `remove`. [Something similar was done in Components](https://github.com/angular/components/pull/23592) some time ago and there haven't been any bug reports as a result.
PR Close#57203
remove the following utilities used in unit tests which check for features
that are supported by all supported browsers:
- supportsCustomElements
- supportsWebAnimation
- supportsRegExUnicodeFlag
- supportsTemplateElement
also remove the following utilities which check for features that are
not supported (and aren't going to be) by any of the supported browsers:
- supportsDeprecatedCustomCustomElementsV0
- supportsDeprecatedShadowDomV0
PR Close#47543
