treewide: get rid of invalid buildPhases argument

I don't know where this comes from (I accidentally did that as well
once), but some derivations seem to use `buildPhases` rather than
`phases` in their derivations.

This kills all improper usages as the lack of a `phases` argument
didn't break the build, so this can be safely removed.

pkgs/shells/lambda-mod-zsh-theme/default.nix

@@ -10,8 +10,6 @@ stdenv.mkDerivation {
     rev = "61c373c8aa5556d51522290b82ad44e7166bced1";
   };
 
-  buildPhases = [ "unpackPhase" "installPhase" ];
-
   installPhase = ''
     mkdir -p $out/share/themes
     cp lambda-mod.zsh-theme $out/share/themes

pkgs/shells/zsh-autosuggestions/default.nix

@@ -15,8 +15,6 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ zsh ];
 
-  buildPhases = [ "unpackPhase" "installPhase" ];
-
   installPhase = ''
     install -D zsh-autosuggestions.zsh \
       $out/share/zsh-autosuggestions/zsh-autosuggestions.zsh