Auto merge of #132479 - compiler-errors:fx-feat-yeet, r=fee1-dead

Yeet the `effects` feature, move it onto `const_trait_impl`

This PR merges the `effects` feature into the `const_trait_impl` feature. There's really no need to have two feature gates for one feature.

After this PR, if `const_trait_impl` **is** enabled:
* Users can use and define const traits
* `HostEffect` const conditions will be enforced on the HIR
* We re-check the predicates in MIR just to make sure that we don't "leak" anything during MIR lowering

And if `const_trait_impl` **is not** enabled:
* Users cannot use nor define const traits
* `HostEffect` const conditions are not enforced on the HIR
* We will raise a const validation error if we call a function that has any const conditions (i.e. const traits and functions with any `~const` in their where clasues)

This should be the last step for us to be able to enable const traits in the standard library. We still need to re-constify `Drop` and `Destruct` and stuff for const traits to be particularly *useful* for some cases, but this is a good step :D

r? fee1-dead
cc `@rust-lang/project-const-traits`

1 files changed, 1 insertions, 2 deletions

diff --git a/tests/rustdoc/const-effect-param.rs b/tests/rustdoc/const-effect-param.rs
index 3c81700ba83..cceb0adac30 100644
--- a/tests/rustdoc/const-effect-param.rs
+++ b/tests/rustdoc/const-effect-param.rs
@@ -1,8 +1,7 @@
 // Check that we don't render host effect parameters & arguments.
 
 #![crate_name = "foo"]
-#![feature(effects, const_trait_impl)]
-#![allow(incomplete_features)]
+#![feature(const_trait_impl)]
 
 #[const_trait]
 pub trait Tr {