config: eliminate trace flavor
    
    With the tracing options synced to the other flavors, we can eliminate
    the trace flavor entirely.
    
    This implicitly disables the following options that used to be set
    in the trace flavors:
    
    IRQSOFF_TRACER: carries a substantial runtime overhead
    MMIOTRACE: really only needed for driver development
    FTRACE_SELFTEST: introduces noticible delays during boot
    FTRACE_STARTUP_TEST: introduces noticible delays during tracer startup