Remove tor-checkkey

We currently build a tor-checkkey binary in src/tools. It extracts and prints the modulus from a PEM-encoded RSA public key.

Long ago, we added it on order to help detect and clean up the effects of the Debian OpenSSL RNG bug (CVE-2008-0166). But that's nearly a decade ago; maybe we can let this code get removed.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information