docs: minor cleanup in tridiagonal solver

[romanc]

Description

Small PR to improve how the auto-gen docs look like for the tridiagonal solver.

Before	After

Note how deleting the (in) / (out) intent is enabling the auto-docs system to detect the type correctly. Do we need to keep (in) / (out) somewhere?

Also fixes a stale reference (in docs) to the previous NDSLNamelist, which was removed with PR #297.

How has this been tested?

By building docs locally.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas: N/A
• I have made corresponding changes to the documentation (e.g. add new modules to docs/docstrings/)
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules: N/A
• New check tests, if applicable, are included: N/A

[FlorianDeconinck]

Let's bring the in/out thing at stand up - we put it everywhere

[romanc]

Let's bring the in/out thing at stand up - we put it everywhere

Sounds good - I'm not particularly against it. The way it's done now (i.e. the way it was copied over from the Fortran), it overrides any type that might have been detected.