Auto merge of rust-lang#85457 - jyn514:remove-doc-include, r=GuillaumeGomez

Remove `doc(include)`

This nightly feature is redundant now that `extended_key_value_attributes` is stable (rust-lang#83366). `@rust-lang/rustdoc` not sure if you think this needs FCP; there was already an FCP in rust-lang#82539, but technically it was for deprecating, not removing the feature altogether.

This should not be merged before rust-lang#83366.

cc `@petrochenkov`

Author: bors

core/src/lib.rs

@@ -159,7 +159,6 @@
 #![feature(const_fn_transmute)]
 #![feature(abi_unadjusted)]
 #![feature(adx_target_feature)]
-#![feature(external_doc)]
 #![feature(associated_type_bounds)]
 #![feature(const_caller_location)]
 #![feature(slice_ptr_get)]