Cleanup after migration of P4BBI from Classic to Streams.
Updated README.md to indicate that P4BBI has moved to the //p4bbi
depot. Removed all other files in dev, main, tools, and downloads
directories.
Before this change:
* //p4bbi/main has been populated.
* Swarm project branches were updated to use //p4bbi/main paths.
* //guest/perforce_software/p4bbi/dev/... and //guest/perforce_software/p4bbi/main/...
were identical.
* //guest/perforce_software/p4bbi/tools/... is moved to //p4bbi/main/tools/...
* A new //p4bbi/main/downloads was created.