chore(fusion): remove duplicate oracle_mode implementation (issue #344)

The oracle-mode tournament is implemented in oracle.go/oracle_test.go and
wired through tournament.go, loopbuilder, agentloop, and config. The
standalone oracle_mode.go/oracle_mode_test.go were an alternative
implementation that was never connected to the system; delete them to avoid
confusion and dead code.

Author: SIN CI