ENH: Remove use of include <vtksys/stl/*> and vtksys_stl::*

We no longer need this compatibility layer for the compilers we support.
Use the following commands to switch to standard header and namespace:

 git grep -l vtksys/stl/ | xargs sed -i 's|vtksys/stl/||'
 git grep -l vtksys_stl | xargs sed -i 's|vtksys_stl|std|g'