Remove the `jumpabsolute` member from `mstatement_s`.

Remove the `jumpabsolute` member from `mstatement_s`.

This reduces the struct from 20 to 16 bytes, and thus may save some
RAM. It also may improve CPU cache behavior by keeping more QC code in
L1 and L2 cache, and possibly also improve instruction processing inside
the CPU as all statements are aligned the same way.

On `srv04`, this speeds up Xonotic's `serverbench` from 58.92s real,
57.72s user to 57.72s real, 56.59s user (median of 25).