Stripping sequence in `SUMMARIZE_RESULTS` is errorneous for complex mods

[jonasscheid]

Description of the bug

Complex mods are not correctly stripped such as

peptidoform	sequence
FL(Label:13C(6)15N(1))ASSEGGFTK	FL(13C(6)15N(1))ASSEGGFTK

I specified --variable_mods 'Oxidation (M),Label:13C(6)15N(1) (L)' as CLI flag

we might need to use pyopens functionality to deal with this