[SYCL] re-enable Scheduler StreamBufferDeallocation unit test (#15292)

A month ago, we had a strange intermittent failure of one of the unit
tests: #15049 and in response to
that we disabled the test. It is unclear why that might have been
failing.

But that was when there were some other disrupting changes, and fallout
from that has since been fixed.


I have retested this on Windows for 100,000 iterations, and not a single
failure seen. Tested on the CI, ran successfully there too.

I'd like to reenable this test with this PR. If the CI system starts
failing on PR, we can just revert this PR in coming days.

Author: cperkinsintel

sycl/unittests/scheduler/GraphCleanup.cpp

@@ -307,12 +307,7 @@ struct AttachSchedulerWrapper {
 };
 
 // Check that stream buffers are released alongside graph cleanup.
-// https://github.com/intel/llvm/issues/15049
-#ifdef _WIN32
-TEST_F(SchedulerTest, DISABLED_StreamBufferDeallocation) {
-#else
 TEST_F(SchedulerTest, StreamBufferDeallocation) {
-#endif
   unittest::UrMock<> Mock;
   platform Plt = sycl::platform();
   context Ctx{Plt};