Remove leftover of type ascription feature gating

[chenyukang]

Fixes #111325

r? @Nilstrieb

[Noratrieb]

Note: this removed the language feature gate, but the built-in macro creates a library feature gate of the same name, which doesn't conflict.

[cjgillot]

Should the feature be declared in rustc_feature::removed?

[Noratrieb]

I wonder how well that interacts with the library feature. Maybe we should just keep the feature, but you can try moving it to removed.

[chenyukang]

we also didn't remove it from AST right now, there are multiple test case is changed to use type_ascribe!, maybe we should keep it at this moment.

[cjgillot]

Should the feature be declared in rustc_feature::removed?

[Noratrieb]

Let's keep the feature definition, but the removal of the gating code looks good.
r=me after reading the definition

[chenyukang]

@bors r=Nilstrieb

[bors]

📌 Commit 8baa32f has been approved by Nilstrieb

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8baa32f with merge 7d5b746...

[bors]

☀️ Test successful - checks-actions
Approved by: Nilstrieb
Pushing 7d5b746 to master...

[rust-timer]

Finished benchmarking commit (7d5b746): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.6%	[-2.6%, -2.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.6%	[-2.6%, -2.6%]	1

Cycles

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.2%	[-1.2%, -1.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.2%	[-1.2%, -1.2%]	1

Binary size

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

Bootstrap: 648.734s -> 647.604s (-0.17%)