KERN_PROC_VM_LAYOUT sysctl: fix bug in 32-bit-compatible path

vmspace_free() is called redundantly in the 32-bit-compatible
path in sysctl_kern_proc_vm_layout(), causing a premature free
(possibly for the current address space). Remove the extra call.

PR: 272401
Reported by: marklmi at yahoo.com
Reviewed by: markj
Differential Revision: https://reviews.freebsd.org/D40908