TST: Remove dead code for LogFormatterSciNotation test

`LogFormatterSciNotation.sublabel` is not an attribute that exists.
There is the private `LogFormatterSciNotation._sublabels`, but this
obviously doesn't need to be set as the test is already passing.

Author: QuLogic

lib/matplotlib/tests/test_ticker.py

@@ -971,7 +971,6 @@ class TestLogFormatterSciNotation:
     @pytest.mark.parametrize('base, value, expected', test_data)
     def test_basic(self, base, value, expected):
         formatter = mticker.LogFormatterSciNotation(base=base)
-        formatter.sublabel = {1, 2, 5, 1.2}
         with mpl.rc_context({'text.usetex': False}):
             assert formatter(value) == expected