swift234

[build-script] Remove direct setting of the cmake variable LLVM_INCLUDE_TESTS via SOURCE_TREE_CINDLUES_TESTS. It is by default set to True and we turn it off via the variable LLVM_INCLUDE_TESTS now.

This actually became a no-op since the build-script-impl triggered instance of
LLVM_INCLUDE_TESTS is always put strictly after this instance of setting the
cmake variable on the cmake line.