perfetto-ui: Remove 'Tracks' header panel
perfetto-ui: Remove 'Tracks' header panel

Almost everything is tracks and having the header makes is super
confusing when you pin a track.

Change-Id: I18bd6eed961c9e16559006fc7e69b78216d11a66
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto