ui: Don't add ftrace tab by default

- The ftrace plugin makes the ftrace tab a "default" tab when the trace
  contains ftrace events, which means the tab is shown on trace load.
- Most traces have ftrace events, which means most folks get this tab
  appearing the moment they open a trace.
- This tab is not that important for most users, so this could add
  confusion, and waste vertical real estate.
- This CL stops showing this tab by default. Users must find it in the
  tab dropdown or by using the command.

Change-Id: I4dd26e3e95c1c808ba10ca15dbaf16b7a64d3836