Fix build error

Error was:

  CMake Error at third-party/libzip/regress/CMakeLists.txt:216 (ADD_CUSTOM_TARGET):
    ADD_CUSTOM_TARGET cannot create target "check" because another target with
    the same name already exists.  The existing target is a custom target
    created in source directory
    "third-party/capnproto/c++/src".
  See documentation for policy CMP0002 for more details.

openai/third-party/capnproto/c++/src/CMakeLists.txt

@@ -38,9 +38,6 @@ if(BUILD_TESTING)
     set(CAPNP_INCLUDE_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
     #TODO(someday) It would be nice to use targets instead of variables in CAPNP_GENERATE_CPP macro
   endif()
-
-  # Sadly, we can't use the 'test' target, as that's coopted by ctest
-  add_custom_target(check "${CMAKE_CTEST_COMMAND}" -V)
 endif()  # BUILD_TESTING
 
 # kj ===========================================================================