(#20801) allow */* wildcard

Curl sends an "Accept: */*" header by default, which matches
"application/json", according to the RFCs. This patches allows this
wildcard to be accepted when interacting with puppetdb's REST API.
doc: remove Accept header from examples

Since d9634b09c it's no longer required to explicitly set the Accept
header when using curl. The examples can thus be slightly simplifed.
Remove Accept: header from curl tests

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #529 from mfournier/accept-wildcard

Accept wildcard