Drop alias `reduce` for `fold` - we have a `reduce` function

Searching for "reduce" currently puts the `reduce` alias for `fold`
above the actual `reduce` function. The `reduce` function already has a
cross-reference for `fold`, and vice versa.

Drop alias `reduce` for `fold` - we have a `reduce` function

Searching for "reduce" currently puts the `reduce` alias for `fold`
above the actual `reduce` function. The `reduce` function already has a
cross-reference for `fold`, and vice versa.

Drop alias `reduce` for `fold` - we have a `reduce` function

Searching for "reduce" currently puts the `reduce` alias for `fold`
above the actual `reduce` function. The `reduce` function already has a
cross-reference for `fold`, and vice versa.

Drop alias `reduce` for `fold` - we have a `reduce` function

Searching for "reduce" currently puts the `reduce` alias for `fold`
above the actual `reduce` function. The `reduce` function already has a
cross-reference for `fold`, and vice versa.

Rollup of 10 pull requests

Successful merges:

 - rust-lang#84451 (Use flex more consistently)
 - rust-lang#84590 (Point out that behavior might be switched on 2015 and 2018 too one day)
 - rust-lang#84682 (Don't rebind in `transitive_bounds_that_define_assoc_type`)
 - rust-lang#84683 (Minor grammar tweaks for readability to btree internals)
 - rust-lang#84688 (Remove unnecessary CSS rules for search results)
 - rust-lang#84690 (Remove unneeded bottom margin on search results)
 - rust-lang#84692 (Link between std::env::{var, var_os} and std::env::{vars, vars_os})
 - rust-lang#84705 (make feature recommendations optional)
 - rust-lang#84706 (Drop alias `reduce` for `fold` - we have a `reduce` function)
 - rust-lang#84713 (Fix labels for regression issue template)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup