python: remove ncurses flag

It seems the additional linker flags were added in 9d3b0a2 (May 2008) as
a workaround for readline support. They were kept since then, but it
also means that `python3-config` outputs these flags

```console
$ python3-config --libs
 -lpthread -ldl -lcrypt -lncurses -lutil -lm -lm
```

while other GNU/Linux distros do not. For example, Debian 11:

```console
$ sudo apt install python3-dev
$ python3-config --libs
 -lcrypt -lpthread -ldl  -lutil -lm -lm
```

This change removes the `-lncurses` flag and aligns Nix/NixOS with other
distros.

pkgs/development/interpreters/python/cpython/default.nix

@@ -282,7 +282,7 @@ in with passthru; stdenv.mkDerivation {
 
   CPPFLAGS = concatStringsSep " " (map (p: "-I${getDev p}/include") buildInputs);
   LDFLAGS = concatStringsSep " " (map (p: "-L${getLib p}/lib") buildInputs);
-  LIBS = "${optionalString (!stdenv.isDarwin) "-lcrypt"} ${optionalString (ncurses != null) "-lncurses"}";
+  LIBS = "${optionalString (!stdenv.isDarwin) "-lcrypt"}";
   NIX_LDFLAGS = lib.optionalString stdenv.cc.isGNU ({
     "glibc" = "-lgcc_s";
     "musl" = "-lgcc_eh";