Testsuite: mark T4945 as expect_broken (#4945)

In commit 7d519dab, the file
T4945.stdout was added to the repository, to make T4945 pass
validatation presumably.

When that test produces output however, there is a bug somewhere, and we
shouldn't hide it. There is a comment in the Makefile which says:

    "When SpecConstr works there are no STUArrays at all"

So here we remove T4945.stdout again, mark T4945 as expect_broken, and
reopen the ticket.

Differential Revision: https://phabricator.haskell.org/D976

Conflicts:
	testsuite/tests/simplCore/should_compile/T4945.stdout
	testsuite/tests/simplCore/should_compile/all.T

testsuite/tests/simplCore/should_compile/T4945.stdout

-                               -> STUArray RealWorld Int Int
-                              (ipv3 [OS=OneShot] :: STUArray RealWorld Int Int) ->
-                                          case ipv3 of _ [Occ=Dead] { STUArray ds5 ds6 dt ds7 ->
-                                  (Data.Array.Base.STUArray
-                                  (Data.Array.Base.STUArray
-                                  (Data.Array.Base.STUArray
-                                  (Data.Array.Base.STUArray

testsuite/tests/simplCore/should_compile/all.T

@@ -108,7 +108,7 @@ test('T4918',
      ['$MAKE -s --no-print-directory T4918'])
 
 test('T4945',
-     when(compiler_lt('ghc', '7.1'), expect_fail),
+     normal,
      run_command,
      ['$MAKE -s --no-print-directory T4945'])