Remove *MetricFn

[bjorn3]

fixes #44808

[rust-highfive]

r? @kennytm

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[kennytm]

CI is failing.

[00:04:17] error: unused import: `std::collections::BTreeMap`
[00:04:17]   --> /checkout/src/libtest/lib.rs:60:5
[00:04:17]    |
[00:04:17] 60 | use std::collections::BTreeMap;
[00:04:17]    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:04:17]    |
[00:04:17] note: lint level defined here
[00:04:17]   --> /checkout/src/libtest/lib.rs:35:9
[00:04:17]    |
[00:04:17] 35 | #![deny(warnings)]
[00:04:17]    |         ^^^^^^^^
[00:04:17]    = note: #[deny(unused_imports)] implied by #[deny(warnings)]
[00:04:17] 
[00:04:17] error[E0609]: no field `metrics` on type `&mut ConsoleTestState<T>`
[00:04:17]    --> /checkout/src/libtest/lib.rs:892:28
[00:04:17]     |
[00:04:17] 892 |                         st.metrics.insert_metric(test.name.as_slice(),
[00:04:17]     |                            ^^^^^^^
[00:04:17] 
[00:04:17] error: aborting due to 2 previous errors
[00:04:17] 
[00:04:17] error: Could not compile `test`.

[kennytm]

@bors r+ rollup

cc #19145.

[bors]

📌 Commit 83c08d2 has been approved by kennytm

[bors]

⌛ Testing commit 83c08d2 with merge 2537a49...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: kennytm
Pushing 2537a49 to master...