linuxHeaders: cleanup android

compared output and the build log and python2 is not required

both build

'pkgsCross.aarch64-android.linuxHeaders'
'pkgsCross.aarch64-android.bionic.linuxHeaders'

linux-headers> LEX scripts/kconfig/lexer.lex.c
linux-headers> sh: line 1: flex: command not found

linux-headers> YACC scripts/kconfig/parser.tab.[ch]
linux-headers> sh: line 1: bison: command not found

linux-headers> INSTALL ./usr/include
linux-headers> sh: line 1: rsync: command not found

Co-authored-by: exarkun <[e-mail]>

pkgs/os-specific/linux/kernel-headers/default.nix

···
 { stdenvNoCC, lib, buildPackages, fetchurl, perl, elf-header
-, bison ? null, flex ? null, python ? null, rsync ? null
+, bison, flex, rsync
 , writeTextFile
 }:
-
-assert stdenvNoCC.hostPlatform.isAndroid ->
-  (flex != null && bison != null && python != null && rsync != null);
 
 let
 
···
     nativeBuildInputs = [
       perl elf-header
     ] ++ lib.optionals stdenvNoCC.hostPlatform.isAndroid [
-      flex bison python rsync
+      bison flex rsync
     ] ++ lib.optionals (stdenvNoCC.buildPlatform.isDarwin &&
                         stdenvNoCC.hostPlatform.isMips) [
       darwin-endian-h