[lit] Relax NSString test by not checking the REPL welcome message, NFC
[lit] Relax NSString test by not checking the REPL welcome message, NFC

This NSString-in-REPL test was checking the text of the REPL welcome
message, which is a little brittle, and was broken by a change which
added a newline.

It seems simpler to not check the welcome text at all.

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb