contrib: update libupnp to 1.8.7

libupnp 1.6 is starting to get really old and caused bugs recently with
the new winpthread rework for contribs. Bumping to 1.8 should be good
enough for now as it provides a lot of fixes and removes the need for
some patches applied upstream a while ago.

Removed contrib patches:
  - 0001-Do-not-try[...]     -> Fixed upstream by 386b7ed7
  - dont_use_down_intf.patch -> Fixed upstream by 1f2e3b88
  - fix_infinite_loop.patch  -> Fixed upstream by 4367cbfa
  - libpthread.patch         -> Fixed locally in rules.mak
  - missing_win32.patch      -> Fixed upstream by 02bb90c5
  - no-getifinfo.patch       -> Fixed upstream by 0296c3cd

Edited patches (mostly to fit the new sources):
  - miniserver.patch
  - upnp-no-debugfile.patch
  - libupnp-win32.patch (Partially fixed upstream)
  - libupnp-win64.patch
  - windows-version-inet.patch
  - libupnp-win32-exports.patch
  - libupnp-pthread-w32-checks.patch
  - use-unicode.patch

Ref !1591
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