vim-patch:8.1.1842: test listed as flaky should no longer be flaky

Problem:    Test listed as flaky should no longer be flaky.
Solution:   Remove Test_popup_and_window_resize from the list of flaky tests.
            (Daniel Hahler, close vim/vim#4807)
9570aacdb8

src/nvim/testdir/runtest.vim

@@ -269,7 +269,6 @@ let s:flaky_tests = [
       \ 'Test_oneshot()',
       \ 'Test_out_cb()',
       \ 'Test_paused()',
-      \ 'Test_popup_and_window_resize()',
       \ 'Test_quoteplus()',
       \ 'Test_quotestar()',
       \ 'Test_reltime()',