sidedata: use revlogv2 requirement in the test helper We are about to drop the requirement dedicated to sidedata (since revlogv2 will support them unconditionally and previous version will not.). To prepare this more we adapt the test code to not use that requirements. Differential Revision: https://phab.mercurial-scm.org/D10615

upgrade: display sidedata before upgrade This is a small gratuitous change that help making the test simpler to understand on its own. Differential Revision: https://phab.mercurial-scm.org/D10614

revlog: determine sidedata support based on the revlog version Revlog version "2" support sidedata, previous version does not. So lets make the initialization simpler. Differential Revision: https://phab.mercurial-scm.org/D10613

requirements: no longer drop `generaldelta` requirement with revlogv2 A repository could use a mix of revlogv1 and revlogv2, making the requirements still necessary. Overall we should move away from the "requirements" file being used a way to configure the repository and stick to it "what do you need to access this repository". However this is a wider work for another time. In addition the logic we just dropped was confusing the `hg debugformat` command, breaking the upgrade code and inconsistent (eg: `sparse-revlog` is also implied by `revlogv2`). Finally, multiple other config option would imply the use of the `revlogv2` requirements, without drop the `generaldelta` one, leading to more inconsistency. Differential Revision: https://phab.mercurial-scm.org/D10612