Revert "XFAIL test under Linux"

This reverts commit a8e1409.

Author: adrian-prantl

lldb/test/API/lang/swift/union/TestSwiftCUnion.py

@@ -11,7 +11,6 @@ class TestSwiftCUnion(lldbtest.TestBase):
     mydir = lldbtest.TestBase.compute_mydir(__file__)
 
     @swiftTest
-    @expectedFailureAll(oslist=['linux'], bugnumber='rdar://104681366')
     def test_c_unions(self):
         self.build()
         target, process, thread, bkpt = lldbutil.run_to_source_breakpoint(