firefox-wrapper: fix icon linking

[xeji]

Motivation for this change

Fix #39134 . When building firefox-esr, wrapper.nix tried to symlink nonexistent 64x64 and 128x128 icons (these exist in regular firefox but not in esr).

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

[xeji]

@GrahamcOfBorg build firefox-esr firefox

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: firefox-esr, firefox

Partial log (click to expand)

  /nix/store/zc0qa5ycn72vhjvq5glqf8hb8w5sq50x-adwaita-icon-theme-3.28.0
copying path '/nix/store/zc0qa5ycn72vhjvq5glqf8hb8w5sq50x-adwaita-icon-theme-3.28.0' from 'https://cache.nixos.org'...
copying path '/nix/store/v11ahm04zj4dzl7l0jfq1i10i2z2gy86-libcanberra-0.30' from 'https://cache.nixos.org'...
copying path '/nix/store/mnapgaq40ypbs2b4pirkrcd7ngrxlx6w-libnotify-0.7.7' from 'https://cache.nixos.org'...
copying path '/nix/store/7kjp1yw1i0nzyf4rpmzxmlmv6d1zc2kx-firefox-esr-unwrapped-52.7.3esr' from 'https://cache.nixos.org'...
copying path '/nix/store/cy1kq59gs44v3clnwgxgxj3a45q3vg3r-firefox-unwrapped-59.0.2' from 'https://cache.nixos.org'...
building '/nix/store/8yy7zk14nw57aj4cpnj2a4l05y1b9ihr-firefox-59.0.2.drv'...
building '/nix/store/a5a2wcs288rdcsi4zppnfaz3bdciwn7l-firefox-52.7.3esr.drv'...
/nix/store/qn90rymmpfn4dclnlxp63hcc1xrplsr5-firefox-52.7.3esr
/nix/store/m7j86jh7nzkjxzfz1xsa2xiv9rwirvj6-firefox-59.0.2

[GrahamcOfBorg]

Failure on aarch64-linux (full log)

Attempted: firefox-esr, firefox

Partial log (click to expand)

4393 |     let name = unsafe { Atom::from((&*name)) };
     |                                    ^^^^^^^^ help: remove these parentheses
     |
     = note: #[warn(unused_parens)] on by default

   Compiling gkrust-shared v0.1.0 (file:///build/mozilla-release-239e434d6d2b8e1e2b697c3416d1e96d48fe98e5/toolkit/library/rust/shared)
   Compiling gkrust v0.1.0 (file:///build/mozilla-release-239e434d6d2b8e1e2b697c3416d1e96d48fe98e5/toolkit/library/rust)
building of '/nix/store/aygvm68grdm09d5xn6rs8wx2svdjzg8i-firefox-unwrapped-59.0.2.drv' timed out after 3600 seconds
cannot build derivation '/nix/store/hn0r5abm58m19fgsj7b2cm8nih34x54l-firefox-59.0.2.drv': 1 dependencies couldn't be built
�[31;1merror:�[0m build of '/nix/store/hn0r5abm58m19fgsj7b2cm8nih34x54l-firefox-59.0.2.drv' failed

[xeji]

aarch64 failure is unrelated.