ENH: Remove use of include <vtksys/ios/*> and vtksys_ios::*

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/ios/ | xargs sed -i 's|vtksys/ios/||'
 git grep -l vtksys_ios | xargs sed -i 's|vtksys_ios|std|g'