Drop workaround for builtin_zlib=ON in LLVM

interpreter/CMakeLists.txt

@@ -56,11 +56,6 @@ elseif(cxx14)
   set(LLVM_ENABLE_CXX1Y ON CACHE BOOL "" FORCE)
 endif()
 
-if(builtin_zlib)
-  set(ZLIB_INCLUDE_DIR ${CMAKE_BINARY_DIR}/include CACHE BOOL "" FORCE)
-  set(ZLIB_LIBRARY ${CMAKE_BINARY_DIR}/lib/libZLIB.a CACHE BOOL "" FORCE)
-endif()
-
 # The llvm::ReverseIterate<bool>::value symbol from llvm's SmallPtrSet.h
 # somehow lands in our cling libraries on OS X and doesn't get hidden
 # by visibility-inlines-hidden, so we suddenly have a global weak symbol