Revert "x86/mm: ensure L2 is always freed if empty"

CI says no:

  https://gitlab.com/xen-project/hardware/xen/-/jobs/8240163332

This reverts commit a6dba2761e.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/mm.c

@@ -5717,7 +5717,7 @@ int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
 
             v += 1UL << L2_PAGETABLE_SHIFT;
             v &= ~((1UL << L2_PAGETABLE_SHIFT) - 1);
-            goto check_l3;
+            continue;
         }
 
         if ( l2e_get_flags(*pl2e) & _PAGE_PSE )