teams: Do $PATH lookup in teams.desktop instead of hardcoding derivation

See db236e588d "steam: Do $PATH lookup in steam.desktop [...]".
tl;dr: Otherwise widget/panel/desktop icons in DEs like KDE break.

I verified that there are no other (executable) paths in the .desktop
file and therefore went for this minimal diff.

pkgs/applications/networking/instant-messengers/teams/default.nix

@@ -47,7 +47,7 @@ stdenv.mkDerivation rec {
     mv share $out/share
 
     substituteInPlace $out/share/applications/teams.desktop \
-      --replace /usr/bin/ $out/bin/
+      --replace /usr/bin/ ""
 
     ln -s $out/opt/teams/teams $out/bin/