[SDK] Remove the obsolete XCTest overlay

The actual XCTest overlay has not been maintained in this repository for years. (It is distributed in Xcode (libXCTestSwiftSupport.dylib), along with XCTest.framework itself.)

The code we have here is badly out of date, and the fact that we have it on the module path in CI makes it interfere with the contents of recent SDKs.

Remove the XCTest overlay from this repository; pick it up from the SDK instead.

rdar://76915582

Author: lorentey

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -965,11 +965,6 @@ function(_add_swift_target_library_single target name)
       endif()
     endif()
 
-    # Always use @rpath for XCTest
-    if(module_name STREQUAL "XCTest")
-      set(install_name_dir "@rpath")
-    endif()
-
     if(SWIFTLIB_SINGLE_DARWIN_INSTALL_NAME_DIR)
       set(install_name_dir "${SWIFTLIB_SINGLE_DARWIN_INSTALL_NAME_DIR}")
     endif()
@@ -1914,9 +1909,7 @@ function(add_swift_target_library name)
       # These paths must come before their normal counterparts so that when compiling
       # macCatalyst-only or unzippered-twin overlays the macCatalyst version
       # of a framework is found and not the Mac version.
-      if(maccatalyst_build_flavor STREQUAL "ios-like"
-          OR (name STREQUAL "swiftXCTest"
-            AND maccatalyst_build_flavor STREQUAL "zippered"))
+      if(maccatalyst_build_flavor STREQUAL "ios-like")
 
         # The path to find iOS-only frameworks (such as UIKit) under macCatalyst.
         set(ios_support_frameworks_path "${SWIFT_SDK_${sdk}_PATH}/System/iOSSupport/System/Library/Frameworks/")

stdlib/public/Darwin/CMakeLists.txt

@@ -19,7 +19,6 @@ set(all_overlays
   Dispatch
   Foundation
   ObjectiveC
-  XCTest
 )
 
 if(DEFINED SWIFT_OVERLAY_TARGETS)