remove redundant path spec for vtzero's dependency on protozero

Summary: was interfering with construction of alternate third-party directory structure. tested on all build/target combinations

Reviewed By: leapally

Differential Revision: D60083427

fbshipit-source-id: 2327086ab5535a24f3177edf3428306e42ed78ae

build/cmake/third-party/vtzero.cmake

@@ -6,8 +6,6 @@
 message(CHECK_START "vtzero")
 list(APPEND CMAKE_MESSAGE_INDENT "  ")
 
-set(PROTOZERO_INCLUDE_DIR "${CMAKE_INSTALL_PREFIX}/include")
-
 find_package(Git REQUIRED)
 
 CPMAddPackage(