KVM: Documentation: remove VM mmap documentation

Since commit 80f5b5e7 ("KVM: remove vm mmap method"), the VM mmap
handler is gone. Remove the corresponding documentation.
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virtual/kvm/api.txt

@@ -110,11 +110,7 @@ Type: system ioctl
 Parameters: machine type identifier (KVM_VM_*)
 Returns: a VM fd that can be used to control the new virtual machine.
 
-The new VM has no virtual cpus and no memory.  An mmap() of a VM fd
-will access the virtual machine's physical address space; offset zero
-corresponds to guest physical address zero.  Use of mmap() on a VM fd
-is discouraged if userspace memory allocation (KVM_CAP_USER_MEMORY) is
-available.
+The new VM has no virtual cpus and no memory.
 You probably want to use 0 as machine type.
 
 In order to create user controlled virtual machines on S390, check