clapper: remove workaround for undeclared gio-unix-2.0
clapper: remove workaround for undeclared gio-unix-2.0

As of upstream's commit "Fix missing gio-unix-2.0 dep"
https://github.com/Rafostar/clapper/commit/2500a422860887d9d165af26731fe6199c3baa14
we no longer need to specify this ourselves.

See https://github.com/NixOS/nixpkgs/issues/36468 for the
NixOS-wide tracking of undeclared gio-unix-2.0 workarounds.

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