protover: Using twice the same version for old tor

protover_compute_for_old_tor() checks twice 0.2.7.5 version leading to dead code.

According to the comment and the spec, it should be 0.2.9.1-alpha.

  } else if (tor_version_as_new_as(version, "0.2.7.5")) {
    /* 0.2.9.1-alpha HSRend=2 */
    return "Cons=1-2 Desc=1-2 DirCache=1 HSDir=1 HSIntro=3 HSRend=1-2 "
      "Link=1-4 LinkAuth=1 "
      "Microdesc=1-2 Relay=1-2";

Patch coming up.