Update UR codeowners after removing PI

#14145 added, moved, and removed files
owned by the `unified-runtime-reviewers` team. This patch updates the
CODEOWNERS file accordingly.

.github/CODEOWNERS

@@ -34,8 +34,12 @@ sycl/doc/design/ @intel/llvm-reviewers-runtime
 sycl/doc/design/spirv-extensions/ @intel/dpcpp-spirv-doc-reviewers
 sycl/doc/extensions/ @intel/dpcpp-specification-reviewers
 
-# Unified Runtime 
-sycl/plugins @intel/unified-runtime-reviewers
+# Unified Runtime
+sycl/cmake/modules/FetchUnifiedRuntime.cmake @intel/unified-runtime-reviewers
+sycl/include/sycl/detail/ur.hpp @intel/unified-runtime-reviewers
+sycl/source/detail/posix_ur.cpp @intel/unified-runtime-reviewers
+sycl/source/detail/ur.cpp @intel/unified-runtime-reviewers
+sycl/source/detail/windows_ur.cpp @intel/unified-runtime-reviewers
 sycl/test-e2e/Plugin/ @intel/unified-runtime-reviewers
 
 # Win Proxy Loader