`--no-undo` tests don't work with PyMOL 2.5

[speleo3]

The runall.pml script currently runs tests with --offline --no-mmlibs --no-undo. Removing these flags makes 9 tests fail with PyMOL 2.5.6.

6 of these failures come from --no-undo and these tests seem unsupported by any modern PyMOL version.

FAIL: test (tests/jira/PYMOL-1276_py.Test1276)
FAIL: testUndoAfterRemoveAtomOnDiscrete__0 (tests/jira/PYMOL-1697_py.TestPYMOL1697)
FAIL: testUndoAfterRemoveAtomOnDiscrete__1 (tests/jira/PYMOL-1697_py.TestPYMOL1697)
FAIL: testAtomLevelSettingsOnRemove (tests/jira/PYMOL-1567_py.TestPYMOL1567)
FAIL: testAtomLevelSettingsOnRemove2 (tests/jira/PYMOL-1567_py.TestPYMOL1567)
FAIL: testAtomStateLevelSettingsOnRemove (tests/jira/PYMOL-1567_py.TestPYMOL1567)

I suggest to either fix those tests for the new undo system, or remove them.