metrics: Remove unused features (#2542)

The aging linkerd-metrics crate includes some features that are unused
in our codebase: a histogram Summary; and a 'Scopes' type. Neither of
these are used in our codebase.

This change removes these defunct features so they need not be
considered as we make future improvements/replacements to our metrics
infrastructure.

Cargo.lock

@@ -755,16 +755,6 @@ version = "0.12.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8a9ee70c43aaf417c914396645a0fa852624801b24ebb7ae78fe8272889ac888"
 
-[[package]]
-name = "hdrhistogram"
-version = "7.5.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7f19b9f54f7c7f55e31401bb647626ce0cf0f67b0004982ce815b3ee72a02aa8"
-dependencies = [
- "byteorder",
- "num-traits",
-]
-
 [[package]]
 name = "heck"
 version = "0.4.1"
@@ -1629,7 +1619,6 @@ name = "linkerd-metrics"
 version = "0.1.0"
 dependencies = [
  "deflate",
- "hdrhistogram",
  "http",
  "hyper",
  "linkerd-stack",

linkerd/metrics/Cargo.toml

@@ -8,12 +8,10 @@ publish = false
 
 [features]
 default = []
-summary = ["hdrhistogram"]
 test_util = []
 
 [dependencies]
 deflate = { version = "1", features = ["gzip"] }
-hdrhistogram = { version = "7.5", default-features = false, optional = true }
 http = "0.2"
 hyper = { version = "0.14", features = ["http1", "http2"] }
 linkerd-stack = { path = "../stack", optional = true }

linkerd/metrics/src/lib.rs

@@ -10,22 +10,16 @@ pub mod latency;
 #[cfg(feature = "linkerd-stack")]
 mod new_metrics;
 mod prom;
-mod scopes;
 mod serve;
 mod store;
-#[cfg(feature = "summary")]
-mod summary;
 
 #[cfg(feature = "linkerd-stack")]
 pub use self::new_metrics::NewMetrics;
-#[cfg(feature = "summary")]
-pub use self::summary::Summary;
 pub use self::{
     counter::Counter,
     gauge::Gauge,
     histogram::Histogram,
     prom::{FmtLabels, FmtMetric, FmtMetrics, Metric},
-    scopes::Scopes,
     serve::Serve,
     store::{LastUpdate, SharedStore, Store},
 };