Remove no- prefix from command line flags in rtc_event_log2text and rtc_event_log2rtp_dump and negate their meaning.

BUG=webrtc:8202

Review-Url: https://codereview.webrtc.org/3008113002
Cr-Original-Commit-Position: refs/heads/master@{#19798}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c3d2bfd2443a55f22d84f15f5f64e2ea80daba19