Revert "KVM: x86: Add a WARN on TIF_NEED_FPU_LOAD in kvm_load_guest_fpu()"

This reverts commit 95145c25.
The next few patches will fix the issue so the warning is not
needed anymore; revert it separately to simplify application to
stable kernels.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>