PROTON-2716: replace `include_directories()` call with opentelemetry-cpp provided targets (#394)

diff --git a/cpp/CMakeLists.txt b/cpp/CMakeLists.txt
index 0ef4f54..4127b2f 100644
--- a/cpp/CMakeLists.txt
+++ b/cpp/CMakeLists.txt
@@ -40,7 +40,6 @@
 find_package(opentelemetry-cpp)
 option(ENABLE_OPENTELEMETRYCPP "Use opentelemetry for distributed tracing" ${OPENTELEMETRY-CPP_FOUND})
 if (ENABLE_OPENTELEMETRYCPP)
-  include_directories(${OPENTELEMETRY_CPP_INCLUDE_DIRS})
   set(TRACING_SRC src/tracing_opentelemetry.cpp src/tracing_stub.cpp)
   set(TRACING_LIBS opentelemetry-cpp::trace)
 else()