[libc] delete old hdrgen

[nickdesaulniers]

Now that we have newhdrgen, filing a bug to track the removal of the existing hdrgen (couldn't find an existing bug for this; feel free to dupe this to that if it exists).

I've moved over the buildbots to use newhdrgen (required resetting buildbot's cmakecache).

cc @petrhosek @RoseZhang03 @aaryanshukla

[llvmbot]

@llvm/issue-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Now that we have newhdrgen, filing a bug to track the removal of the existing hdrgen (couldn't find an existing bug for this; feel free to dupe this to that if it exists).

I've moved over the buildbots to use newhdrgen (required resetting buildbot's cmakecache).

cc @petrhosek @RoseZhang03 @aaryanshukla

[aaryanshukla]

Fairly sure no such bug existed before. Let me know if there are any issues with newhdrgen while moving the buildbots.