Remove duplication of table_compute_checksum function

It seems like there was some merge error when first cleaning up and
sharing this function.  We have both an inline version of the function
in include/tables_csum.h and a non-inline version in lib/tables_csum.c.
Rework things so that we only have the non-inline version (due to number
of calls, we should not inline this).

Fixes: 1befb38b ("x86: Move table csum into separate file")
Fixes: 2b445e4d ("x86: Move table csum into separate header")
Cc: Alexander Graf <agraf@csgraf.de>
Signed-off-by: Tom Rini <trini@konsulko.com>