treewide: go: inherit platforms instead of using platforms.all

`buildGoModule` and `buildGoPackage` by default inherit the `platforms`
from go. That seems better than explicitly configuring `platforms.all`.

There are also many packages that specify 'linux + darwin' - this is
even suggested in the documentation. We might also want to update those,
but let's do the noncontroversial change first.

pkgs/development/libraries/boringssl/default.nix

@@ -52,7 +52,6 @@ buildGoModule {
   meta = with lib; {
     description = "Free TLS/SSL implementation";
     homepage    = "https://boringssl.googlesource.com";
-    platforms   = platforms.all;
     maintainers = [ maintainers.thoughtpolice ];
     license = with licenses; [ openssl isc mit bsd3 ];
   };