KVM: VMX: Remove unused declaration of vmx_request_immediate_exit()

After commit 0ec3d6d "KVM: x86: Fully defer to vendor code to decide
how to force immediate exit", vmx_request_immediate_exit() was removed.
Commit 5f18c64 "KVM: VMX: Move out vmx_x86_ops to 'main.c' to dispatch
VMX and TDX" added its declaration by accident.  Remove it.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/r/20240506075025.2251131-1-binbin.wu@linux.intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/x86/kvm/vmx/x86_ops.h

@@ -110,7 +110,6 @@ u64 vmx_get_l2_tsc_offset(struct kvm_vcpu *vcpu);
 u64 vmx_get_l2_tsc_multiplier(struct kvm_vcpu *vcpu);
 void vmx_write_tsc_offset(struct kvm_vcpu *vcpu);
 void vmx_write_tsc_multiplier(struct kvm_vcpu *vcpu);
-void vmx_request_immediate_exit(struct kvm_vcpu *vcpu);
 void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu);
 void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
 #ifdef CONFIG_X86_64