fix: invalid link to go to next page for subsections in contracts guides

[ryabykhms]

While studying this excellent documentation, I noticed that it is impossible to make following transitions by clicking Next:

• https://docs.sablier.com/contracts/v2/guides/local-environment => https://docs.sablier.com/contracts/v2/guides/create-stream/lockup-linear
• https://docs.sablier.com/contracts/v2/guides/create-stream/lockup-dynamic => https://docs.sablier.com/contracts/v2/guides/batch-create-streams/batch-linear-streams

As far as I understand, since the name of the subsection corresponds to the link id specified in the _category_.json, this id can be removed, which solved the problem of moving to the next existent page.

[smol-ninja]

Thank you fro the PR @ryabykhms. You are absolutely right.

[ryabykhms]

This fix solves this issue #54