x86/vector: Remove the macro VECTOR_OFFSET_START

x86/vector: Remove the macro VECTOR_OFFSET_START

Now, Linux uses matrix allocator for vector assignment, the original
assignment code which used VECTOR_OFFSET_START has been removed.

So remove the stale macro as well.

Fixes: commit 69cde0004a4b ("x86/vector: Use matrix allocator for vector assignment")
Signed-off-by: Dou Liyang <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: David Rientjes <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>