refactor(telemetry): Drop the unused ServiceRegistry::getTelemetry()

Nothing on this branch calls it: spans reach the telemetry object
through Telemetry::getInstance(). Removing the pure virtual keeps
ServiceRegistry, and its out-of-tree implementations, unchanged by
telemetry. Consensus tracing, which needs the accessor, declares it on
Application.

include/xrpl/core/ServiceRegistry.h

@@ -24,9 +24,6 @@ class Manager;
 namespace perf {
 class PerfLog;
 }  // namespace perf
-namespace telemetry {
-class Telemetry;
-}  // namespace telemetry
 
 // This is temporary until we migrate all code to use ServiceRegistry.
 class Application;
@@ -227,9 +224,6 @@ public:
     virtual perf::PerfLog&
     getPerfLog() = 0;
 
-    virtual telemetry::Telemetry&
-    getTelemetry() = 0;
-
     // Configuration and state
     [[nodiscard]] virtual bool
     isStopping() const = 0;

src/tests/libxrpl/helpers/TestServiceRegistry.h

@@ -9,7 +9,6 @@
 #include <xrpl/core/ServiceRegistry.h>
 #include <xrpl/ledger/PendingSaves.h>
 #include <xrpl/server/LoadFeeTrack.h>
-#include <xrpl/telemetry/Telemetry.h>
 
 #include <boost/asio/io_context.hpp>
 
@@ -338,12 +337,6 @@ public:
         throw std::logic_error("TestServiceRegistry::getPerfLog() not implemented");
     }
 
-    telemetry::Telemetry&
-    getTelemetry() override
-    {
-        throw std::logic_error("TestServiceRegistry::getTelemetry() not implemented");
-    }
-
     // Configuration and state
     bool
     isStopping() const override

src/xrpld/app/main/Application.cpp

@@ -671,12 +671,6 @@ public:
         return *perfLog_;
     }
 
-    telemetry::Telemetry&
-    getTelemetry() override
-    {
-        return *telemetry_;
-    }
-
     NodeCache&
     getTempNodeCache() override
     {