powerpc: Remove unused paca->pgdir field

The pgdir field in the paca was a leftover from the dynamic VSIDs
patch, and is not used in the current kernel code.  This removes it.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/slb.c

@@ -122,9 +122,6 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
 
 	get_paca()->slb_cache_ptr = 0;
 	get_paca()->context = mm->context;
-#ifdef CONFIG_PPC_64K_PAGES
-	get_paca()->pgdir = mm->pgd;
-#endif /* CONFIG_PPC_64K_PAGES */
 
 	/*
 	 * preload some userspace segments into the SLB.

arch/powerpc/mm/stab.c

@@ -200,10 +200,6 @@ void switch_stab(struct task_struct *tsk, struct mm_struct *mm)
 
 	__get_cpu_var(stab_cache_ptr) = 0;
 
-#ifdef CONFIG_PPC_64K_PAGES
-	get_paca()->pgdir = mm->pgd;
-#endif /* CONFIG_PPC_64K_PAGES */
-
 	/* Now preload some entries for the new task */
 	if (test_tsk_thread_flag(tsk, TIF_32BIT))
 		unmapped_base = TASK_UNMAPPED_BASE_USER32;