gcl: remove asserts

These asserts throw on darwin, before `meta.platforms` is checked. This,
among many others, makes CI require ugly workarounds.

Upstream says its build requirements are "gcc/clang, ..." - so it seems
like these asserts are not required in principle. Also, they are 10
years old.

Can't test, because the packge is marked as broken entirely. Tried
updating to latest 2.7.1, but the build didn't succeed either.

pkgs/development/compilers/gcl/default.nix

@@ -19,11 +19,6 @@
   libXmu,
 }:
 
-assert stdenv ? cc;
-assert stdenv.cc.isGNU;
-assert stdenv.cc ? libc;
-assert stdenv.cc.libc != null;
-
 stdenv.mkDerivation rec {
   pname = "gcl";
   version = "2.6.14";