Revert "Merge pull request #58983 from apple/egorzhdan/cxx-overlay-linux"

[ahoppen]

#58983 caused builds to start failing on CentOS 7 (https://ci.swift.org/job/oss-swift-package-centos-7/582/console) with the following error message. I’m reverting the PR for now to unblock CI.

/home/build-user/swift/stdlib/public/Cxx/std.swift:13:19: error: underlying Objective-C module 'std' not found
@_exported import std // Clang module
                  ^
/home/build-user/swift/stdlib/public/Cxx/String.swift:13:15: error: no type named 'string' in module 'std'
extension std.string {
              ^
/home/build-user/swift/stdlib/public/Cxx/String.swift:23:30: error: no type named 'string' in module 'std'
  public init(cxxString: std.string) {

rdar://94605043