firefox-bin: Avoid including both the wrapped and unwrapped version when using nix run command.

In order to make the man pages accessible, the previous code used
nix-support/propagated-user-env-packages. However this file is also used to set
the PATH when the application is executed with `nix run`, thus including the
wrapped and the wrappee in the environment.

Having the wrappee enumerated first in the environment caused `firefox` to
default to the wrappee, and as such not being able to find a proper GTK. This
was a source of failures while opening a file-picker.

This change removes the code to propagate the wrappe in the environment, as the
man pages are already linked in the wrapper output.

pkgs/applications/networking/browsers/firefox/wrapper.nix

@@ -303,10 +303,6 @@ let
             ln -sLt $out/lib/mozilla/pkcs11-modules $ext/lib/mozilla/pkcs11-modules/*
         done
 
-        # For manpages, in case the program supplies them
-        mkdir -p $out/nix-support
-        echo ${browser} > $out/nix-support/propagated-user-env-packages
-
 
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         #                       #