proxy: remove per client bytes (#5466)

## Problem

Follow up to #5461

In my memory usage/fragmentation measurements, these metrics came up as
a large source of small allocations. The replacement metric has been in
use for a long time now so I think it's good to finally remove this.
Per-endpoint data is still tracked elsewhere

## Summary of changes

remove the per-client bytes metrics

proxy/src/console/messages.rs

@@ -100,31 +100,6 @@ pub struct MetricsAuxInfo {
     pub branch_id: BranchId,
 }
 
-impl MetricsAuxInfo {
-    /// Definitions of labels for traffic metric.
-    pub const TRAFFIC_LABELS: &'static [&'static str] = &[
-        // Received (rx) / sent (tx).
-        "direction",
-        // ID of a project.
-        "project_id",
-        // ID of an endpoint within a project.
-        "endpoint_id",
-        // ID of a branch within a project (snapshot).
-        "branch_id",
-    ];
-
-    /// Values of labels for traffic metric.
-    // TODO: add more type safety (validate arity & positions).
-    pub fn traffic_labels(&self, direction: &'static str) -> [&str; 4] {
-        [
-            direction,
-            &self.project_id,
-            &self.endpoint_id,
-            &self.branch_id,
-        ]
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;