vm: Eliminate a redundant call to vm_reserv_break_all()

When vm_object_collapse() was changed in commit 98087a0 to call
vm_object_terminate(), rather than destroying the object directly, its
call to vm_reserv_break_all() should have been removed, as
vm_object_terminate() calls vm_reserv_break_all().

Reviewed by: kib, markj
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D45495