trace2: emit 'def_param' set with 'cmd_name' event

trace2: emit 'def_param' set with 'cmd_name' event

Some commands do not cause a set of 'def_param' events to be emitted.
This includes "git-remote-https", "git-http-fetch", and various
"query" commands, like "git --man-path".

Since all of these commands do emit a 'cmd_name' event, add code to
the "trace2_cmd_name()" function to generate the set of 'def_param'
events.

Remove explicit calls to "trace2_cmd_list_config()" and
"trace2_cmd_list_env_vars()" in git.c since they are no longer needed.

Reviewed-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>