Unbundle libzip

[nikic]

Since #3531 we're testing on Xenial, which has a sufficiently recent libzip, so we should be able to move ahead with the unbundling.

/cc @remicollet

[KalleZ]

cc @weltling for Windows parts of things as I'm not sure if the buildbot uses the bundled libzip or not

[nikic]

IIRC support for the bundled libzip has already been dropped from the win32 build system in PHP 7.3.

[KalleZ]

@nikic Ah yes, it seems to be the case: 757789e

[nikic]

AppVeyor failure is spurious, so this should be good to go.

[weltling]

External libzip is already in use for 7.2 actually, the bundled one wasn't updated since then. Lower versions don't support encryptiont, even not sure it would compile. Thus, removing the bundled codes is fine.

Thanks.

[nikic]

Aaaand it's gone (c099be4, 4e23dff, 1a55c36).

[remicollet]

@nikic thanks a lot.