[lldb] Don't ask for QOS_CLASS_UNSPECIFIED queue in TestQueues

TestQueues is curiously failing for me as my queue for QOS_CLASS_UNSPECIFIED
is named "Utility" and not "User Initiated" or "Default". While debugging, this
I noticed that this test isn't actually using this API right from what I understand. The API documentation
for `dispatch_get_global_queue` specifies for the parameter: "You may specify the value
QOS_CLASS_USER_INTERACTIVE, QOS_CLASS_USER_INITIATED, QOS_CLASS_UTILITY, or QOS_CLASS_BACKGROUND."

QOS_CLASS_UNSPECIFIED isn't listed as one of the supported values. swift-corelibs-libdispatch
even checks for this value and returns a DISPATCH_BAD_INPUT. The
libdispatch shipped on macOS seems to also check for QOS_CLASS_UNSPECIFIED and seems to
instead cause a "client crash", but somehow this doesn't trigger in this test and instead we just
get whatever queue

This patch just removes that part of the test as it appears the code is just incorrect.

Reviewed By: jasonmolenda

Differential Revision: https://reviews.llvm.org/D86211