The “extentions” are actually internals to Chromium and for some reason they just announce themselves as extensions on Chromium for Linux. Has something to do with how it’s developed I guess.
I wouldn’t want to get rid of any of those if I were you. They’re all quite essential to how Chromium works. If you got rid of the PDF viewer for example, you wouldn’t be able to conveniently open PDF files in your browser anymore.
Check out chrome://flags if you want a slew of experimental options you can play with though. Careful though.
Anyway, I wouldn’t change anything, you’re all good and these aren’t suspect or anything.