[Test] Ignore test infrastucture sources in debugging tests

This solves no immediate deficiency, but is a to-do that arose as part
of an ongoing effort to port the old, slightly too restrictive
checkLocalVariableTable tests to the more "functional" debugger
infrastructure.

This just shaves a little bit of overhead off the test expectations
and couples them less tightly to the specifics of the test
infrastructure.

compiler/testData/debug/stepping/suspendFunWithSuspendLambdaParameter.kt

@@ -13,7 +13,6 @@ suspend fun box() {
 // LINENUMBERS
 // test.kt:8 box
 // test.kt:4 foo
-// CoroutineUtil.kt:28 getContext
 // test.kt:-1 <init>
 // test.kt:-1 create
 // test.kt:-1 invoke