Fix publishing errors

[mmitche]

Fix two errors:
* Remove unneeded signed symbol catalog injection
* Build definition is not importing becuase of duplicated task name.

[mmitche]

@mikem8361 This is also for 2.1. The publishing changes can be applied there too, yes?

[dagood]

Yes, and in 2.1 we're in even better shape because final publish will pick up coreclr/corefx symbol packages and publish those, not just the core-setup outputs.