x86/entry: Cleanup PARAVIRT

Since commit 5c8f6a2e ("x86/xen: Add
xenpv_restore_regs_and_return_to_usermode()") Xen will no longer reach
this code and we can do away with the paravirt
SWAPGS/INTERRUPT_RETURN.
Suggested-by: Andrew Cooper <Andrew.Cooper3@citrix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.756014488@infradead.org

arch/x86/entry/entry_64.S

@@ -608,8 +608,8 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
 
 	/* Restore RDI. */
 	popq	%rdi
-	SWAPGS
-	INTERRUPT_RETURN
+	swapgs
+	jmp	native_iret
 
 
 SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL)