cabal2nix: resolve icu-i18n pkg-config module to icu

[raehik]

The Nix package is icu, which provides three pkg-config modules including icu-i18n.

[raehik]

Question: Are the existing ICU pkg-config module entries correct? development/libraries/icu/base.nix states:

      pkgConfigModules = [
        "icu-i18n"
        "icu-io"
        "icu-uc"
      ];

So maybe we should swap out icui18n, icuuc etc. for icu-i18n, icu-uc. Or maybe we need both, if both are used?

[sternenseemann]

Done in 0365d9b.