[CMake] Don't require json in ROOTConfig if no components specified

If components are not specified, we should assume nlohmann_json is not
required. Propagating the dependency on nlohmann_json just for the sake
of one ROOT feature (ROOTEve) that might be used is unreasonable. We can
expect from the users that link against ROOTEve to list this component
explicitly.

cmake/scripts/ROOTConfig.cmake.in

@@ -112,10 +112,11 @@ if (NOT ROOT_builtin_nlohmannjson_FOUND)
           set(_need_json TRUE)
        endif()
     endforeach()
-  else()
-    # if components not specified - suppose all
-    set(_need_json TRUE)
   endif()
+  # If components are not specified, we assume json is not required.
+  # Propagating the dependency on nlohmann_json just for the sake of one small
+  # ROOT feature that might be used is unreasonable. We can expect from the
+  # users that link against ROOTEve to list this component explicitly.
 endif()
 
 if(_need_json)