Upgrade to libevent 2.1.7-rc again.

  - Previous CL got messed up and then submitted, and actually hadn't
    upgraded to 2.1.7 but in fact left it at 2.1.5 but added other
    changes that added autoconf.
  - Autoconf additions blew out the binary size.
  - Trying here again, but without autoconf, to see what happens with
    Jenkins. Previous build failures that made me think we needed it
    might have been ephemeral and unrelated.

Change-Id: I03ff28eea1275f0a2a1a703a5c112394add19b8a
1 file changed