rustdoc: Masked functions still appear in the search result.

[kennytm]

Repro:

1. Go to nightly docs
2. Search for "aborting" (or just go to https://doc.rust-lang.org/nightly/std/?search=aborting)
3. Note that the functions aborting_div and aborting_rem appeared.
4. Clicking into the result will not jump to any functions.

Expected: aborting_div and aborting_rem should not appear in the search result.

The aborting_div and aborting_rem methods are part of the Int trait in compiler_builtins which is not supposed to be exposed. The documentation about this trait is successfully hidden thanks to #44026, but the search entry still exists.

cc @QuietMisdreavus

[GuillaumeGomez]

Taking a look.

[GuillaumeGomez]

Hum, I thought a check was missing but it doesn't seem to be the case, will require a deeper look.