perfetto-ui: Remove ui/src/panels
perfetto-ui: Remove ui/src/panels

Currently none of the panels live in this directory. If and when we
move them to a directory we can re-add this.

Change-Id: Ic33037f4734d041c02da01a5c60ffa6fa4c9d07d
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto