loader: Don't reserve space for symbols twice.

The current code bumps lastaddr twice for the symbol table
location. However, the first bump is bogus and results in wasted
space. Remove it.

PR: 110995
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D31017

(cherry picked from commit 297e9f364b5aa243572ee52b1faef9b3542c1c9e)