https://bugs.webkit.org/show_bug.cgi?id=272053
rdar://125864015

Reviewed by Alexey Proskuryakov and Jonathan Bedard.

Since WebKit's move to additions SDKs last summer and changes to how
XCBuild loads specifications in 2022, we no longer need to modify Xcode
to build embedded platforms.

* ReadMe.md: Remove reference to the script and merge the Mac / embedded
  build sections, since there is less of a difference between them now.
* Tools/Scripts/configure-xcode-for-embedded-development: Replaced with
  an error message that the script is no longer needed.
* Websites/webkit.org/languages.md: Remove reference to the script.

Canonical link: https://commits.webkit.org/278218@main