media-gfx/ipe, media-gfx/ipe-tools: use virtual/zlib, drop dead blockers

media-gfx/ipe, media-gfx/ipe-tools: use virtual/zlib, drop dead blockers

sys-libs/zlib is deprecated in favor of virtual/zlib (gentoo
profiles/package.deprecated recommends depending on the virtual
unless zlib-ng compat is broken). Also drop the ipe-tools blockers on
media-gfx/{figtoipe,svgtoipe,pdftoipe,ipe5toxml}: none of those
packages exist in this repo, gentoo, guru, or the thirdparty overlay,
and there's no pkgmove history for them, so the blockers can never
trigger.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>