x86/xen: Remove the unused function p2m_index()

The function p2m_index is defined in the p2m.c file, but not called
elsewhere, so remove this unused function.

arch/x86/xen/p2m.c:137:24: warning: unused function 'p2m_index'.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=3557Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20230105090141.36248-1-jiapeng.chong@linux.alibaba.comSigned-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/p2m.c

@@ -134,11 +134,6 @@ static inline unsigned p2m_mid_index(unsigned long pfn)
 	return (pfn / P2M_PER_PAGE) % P2M_MID_PER_PAGE;
 }
 
-static inline unsigned p2m_index(unsigned long pfn)
-{
-	return pfn % P2M_PER_PAGE;
-}
-
 static void p2m_top_mfn_init(unsigned long *top)
 {
 	unsigned i;