KVM: x86: Remove redundant vm_entry_controls_clearbit() call

When emulating exit from long mode, EFER_LMA is cleared with
vmx_set_efer().  This will already unset the VM_ENTRY_IA32E_MODE control
bit as requested by SDM, so there is no need to unset VM_ENTRY_IA32E_MODE
again in exit_lmode() explicitly.  In case EFER isn't supported by
hardware, long mode isn't supported, so exit_lmode() cannot be reached.

Note that, thanks to the shadow controls mechanism, this change doesn't
eliminate vmread or vmwrite.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Message-Id: <20220311102643.807507-3-zhenzhong.duan@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>