Remove more environment variables when launching inferior swift-test binaries from Xcode, so they don't hang while trying to connect to Xcode.  There is already a superior xctest invocation that's using them, and we need to make sure we're not passing them on so that the xctest invocation being invoked by swift-test thinks it's invoked directly from Xcode.  We should possibly be filtering out all environment variables prefixed with "XCTest", or maybe even better, use an allow-list of environment variables to avoid having the environment leaking into the test.
Remove more environment variables when launching inferior swift-test binaries from Xcode, so they don't hang while trying to connect to Xcode.  There is already a superior xctest invocation that's using them, and we need to make sure we're not passing them on so that the xctest invocation being invoked by swift-test thinks it's invoked directly from Xcode.  We should possibly be filtering out all environment variables prefixed with "XCTest", or maybe even better, use an allow-list of environment variables to avoid having the environment leaking into the test.

rdar://68362616

apple/swift-tools-support-core,apple/swift-tools-support-core,apple/swift-tools-support-core,apple/swift-tools-support-core