[memory-infra] docs: Remove reference to --output-format json

The format is no longer supported by Telmetry, and the default
(--output-format html) already produces both results.html and traces.

Bug: 770685
Change-Id: Iafe2a91a928d74fd3ad248957b010793464d5d98
Reviewed-on: https://chromium-review.googlesource.com/692943
Reviewed-by: Ben Hayden <benjhayden@chromium.org>
Commit-Queue: Juan Antonio Navarro PĂ©rez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505636}
1 file changed