Number of jobs should not be set in Makefile

[Topkek-190]

The value of N in -jN depends on many factors and the decision should be ultimately left up to the user

[Topkek-190]

cc: @rouben

[rouben]

The issue with this PR is that it will be difficult to maintain once a new release is available upstream. Remember, this repo is based on the contents of 7Zip/ZIP archives released upstream by the original author, who maintains their own private SubVersion repo for development.

Any ideas on how we can prevent this change from getting squashed with future releases?

[Topkek-190]

Manually merging the Makefile, maybe? Or maybe a patch could be sent to the author(probably the only viable approach). Has any progress been made on the licensing issue?

[Topkek-190]

@rouben I think, since the software hasn't been updated since 2020, it's probably better to make a tag for the current HEAD and then apply some fixes so that if a new version is released on the MDL website then the repo can be updated easily by making a branch at the original head, i.e. the tag.