Revert "[linux-x86] toolchain refresh with downgraded host flex"

This reverts commit 3870f2b5ae39b5a36b309207beb7abc5fb0b18a2.
Revert "[linux-x86] toolchain refresh from cfX toolchain_* repos"

This reverts commit b7b00248a2f7c9b6312fefadb66d92cb426678ae.