Revert "TS-1125: POST's with Expect: 100-continue are slowed by delayed 100 response"

This reverts commit 9da123014382c00bccb1869782a4f2502229a459 because
it breaks traffic_server and traffic_manager sta startup:

  oarfish:trafficserver.git jpeach$ sudo /tmp/ats/bin/traffic_server -T hdr_token
  [TrafficServer] using root directory '/tmp/ats'
  [Apr 17 21:07:16.489] Server {0x7fff745dd310} DEBUG: (hdr_token) Did not find a WKS for '100-continue'
  NOTE: Traffic Server received Kernel Sig 11, Reason: 1
  /tmp/ats/bin/traffic_server - STACK TRACE:
  0   libsystem_platform.dylib            0x00007fff849a85aa _sigtramp + 26
  1   ???                                 0x00007fff00000001 0x0 + 140733193388033
  2   traffic_server                      0x0000000101b1ad25 main + 2453
  3   libdyld.dylib                       0x00007fff890b25fd start + 1
TS-2732: Add url_sig plugin
TS-2732: Update CHANGES file with appropriate authorship that I missed in the previous commit
TS-2120 remove stale_while_revalidate_plugin
TS-2732 Run the code through indent, to follow our coding standards