Remove PolyGenSig since it's always a dummy binder

[compiler-errors]

Coroutines are never polymorphic in their signature. This cleans up a FIXME in the code:

    /// Returns the "coroutine signature", which consists of its yield
    /// and return types.
    ///
    /// N.B., some bits of the code prefers to see this wrapped in a
    /// binder, but it never contains bound regions. Probably this
    /// function should be removed.

[rustbot]

r? @davidtwco

(rustbot has picked a reviewer for you, use r? to override)

[compiler-errors]

r? types

[spastorino]

@bors r+

[bors]

📌 Commit 1ec3ef7 has been approved by spastorino

It is now in the queue for this repository.

[bors]

⌛ Testing commit 1ec3ef7 with merge 670188c...

[bors]

☀️ Test successful - checks-actions
Approved by: spastorino
Pushing 670188c to master...

[rust-timer]

Finished benchmarking commit (670188c): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.3%	[-1.3%, -1.3%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.3%	[0.5%, 2.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-2.5%, 2.0%]	3

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 674.39s -> 676.141s (0.26%)
Artifact size: 314.17 MiB -> 314.20 MiB (0.01%)