Revert "Check that the LLVM runtimes checkout is new enough"

As discussed in the parent commit, this just doesn't work in practice
and breaks real cases (including the default shallow checkout). Instead
just let the build fail if your LLVM checkout is too old.

This reverts commit 2d4d5d0.

pycheribuild/projects/cross/libcxx.py

@@ -600,8 +600,6 @@ def configure(self, **kwargs) -> None:
                 self.add_cmake_options(LIBCXX_ENABLE_ASSERTIONS=True)
                 # Need to export the symbols from debug.cpp to allow linking code that defines _LIBCPP_DEBUG=1
                 self.add_cmake_options(LIBCXX_ENABLE_BACKWARDS_COMPATIBILITY_DEBUG_MODE_SYMBOLS=True)
-        if not GitRepository.contains_commit(self, "f4fdc4f4d9f6903808541645d383be2ee759f400", src_dir=self.source_dir):
-            self.fatal(f"LLVM revision in {self.source_dir} is too old for this target, please update.")
         super().configure(**kwargs)
 
     def compile(self, **kwargs):