Simplify some term search tactics

[kilpkonn]

Working on the paper @phijor found that "Data constructor" tactic could be simplified quite a bit by running it only in the backwards direction. With n+1 rounds it has same coverage as previous implementation in n rounds, however the tactic it self is more simple and also potentially faster as there is less to do.

In a nutshell the idea is to only work with types in the wish-list rather than with any types.

Turns out it is quite a bit faster:

Before:

ripgrep:
Tail Expr syntactic hits: 238/1692 (14%)
Tail Exprs found: 1223/1692 (72%)
Term search avg time: 15ms

nalgebra:
Tail Expr syntactic hits: 125/3001 (4%)
Tail Exprs found: 2143/3001 (71%)
Term search avg time: 849ms

After

ripgrep:
Tail Expr syntactic hits: 246/1692 (14%)
Tail Exprs found: 1209/1692 (71%)
Term search avg time: 8ms

nalgebra:
Tail Expr syntactic hits: 125/3001 (4%)
Tail Exprs found: 2028/3001 (67%)
Term search avg time: 305ms

Also removed niche optimization of removing scope defs from the search space as this wasn't helping much anyway and made code a bit more complex.

[Veykril]

@bors r+

[bors]

📌 Commit 51c3bd2 has been approved by Veykril

It is now in the queue for this repository.

[bors]

⌛ Testing commit 51c3bd2 with merge db69df3...

[bors]

☀️ Test successful - checks-actions
Approved by: Veykril
Pushing db69df3 to master...