Remove request to priming URL

The priming URL request does not seem to be required for
authentication. Removing it speeds up every GraceDB POST
request by 300-400 ms.
10 jobs for no-priming-url in 8 minutes and 45 seconds (queued for 4 minutes and 10 seconds)
latest
Status Name Job ID Coverage
  Build
passed build:debian:jessie #557943

00:03:54

passed build:debian:stretch #557944

00:01:58

passed build:el7 #557942

00:01:19

passed build:tarball #557941

00:00:26

 
  Test
passed docs #557949

00:01:01

passed syntax #557950

00:00:46

passed test:python2.7 #557945

00:00:41

passed test:python3.5 #557946

00:00:38

passed test:python3.6 #557947

00:00:39

passed test:python3.7 #557948

00:00:41