Remove stale comments about holding pageheap_lock.
Remove stale comments about holding pageheap_lock.

We allocate/deallocate the main bucket array with `new`, so holding
pageheap_lock would be incorrect.

PiperOrigin-RevId: 428014510
Change-Id: I34582c2f448f14faaa4144b368bdeb10c23c1cc8

google/tcmalloc,google/tcmalloc,google/tcmalloc