[XHarness] Remove not needed ignore file. (#5456)

Since we support filtering via categories, we do not longer need the
ignore file in these tests.

tests/bcl-test/BCLTests/common-SystemCoreTests.ignore

@@ -1,2 +0,0 @@
-# System.NotSupportedException : Cannot create boxed TypedReference, ArgIterator, or RuntimeArgumentHandle Objects. 
-MonoTests.System.Linq.Expressions.ExpressionTest_Call.Connect319190