export-patches.pl - No longer export simple-leather

simple-leather is integrated into upstream MWDF, and so is no
longer needed as a branch.
Turrets are now constructed from brass.

Previously turrets were constructed from copper, but left
brass corpses, and mentioned brass in their tissue names.
Merge branch 'master' into unified

* master:
  Turrets are now constructed from brass.
  export-patches.pl - No longer export simple-leather