[test] Remove a redundant FIXME. NFC (#26010)

This became redundant after 28bcb86.

Author: kleisauke

test/test_core.py

@@ -1509,10 +1509,6 @@ def test_exceptions_rethrow_missing(self):
   def test_EXPORT_EXCEPTION_HANDLING_HELPERS(self):
     self.set_setting('ASSERTIONS', 0)
     self.set_setting('EXPORT_EXCEPTION_HANDLING_HELPERS')
-    # FIXME Temporary workaround. See 'FIXME' in the test source code below for
-    # details.
-    if self.get_setting('DISABLE_EXCEPTION_CATCHING') == 0:
-      self.cflags.append('-D__USING_EMSCRIPTEN_EXCEPTION__')
 
     self.maybe_closure()
     create_file('main.cpp', '''