fix(telemetry): drop the duplicate protobuf include

The test carried both <xrpl/proto/xrpl.pb.h> and the bare <xrpl.pb.h>.
Both resolve to the same generated header, because the proto helper puts
the generated tree and its prefixed subdirectory on the target, so the
second include expanded to nothing behind the header guard.

The bare form arrived from merging two same-day clang-tidy commits that
added the include with different spellings. Keep the prefixed spelling,
which is what the telemetry headers and the upstream phase branches use.

src/tests/libxrpl/telemetry/TraceContextPropagator.cpp

@@ -17,8 +17,6 @@
 #include <opentelemetry/trace/trace_flags.h>
 #include <opentelemetry/trace/trace_id.h>
 
-#include <xrpl.pb.h>
-
 #include <cstdint>
 #include <cstring>