We were previously allocating MAXCPU structures for several purposes,
but this is generally unnecessary and is quite excessive. We already
are careful to allocate only as many per-CPU tracing buffers as needed;
extend this to other allocations.

For example, in a 2-vCPU VM, the size of a consumer state structure
drops from 64KB to 128B. The size of the per-consumer dts_buffer and
dts_aggbuffer arrays shrink similarly.

No functional change intended.