use build constraints for embed, clean up makefile

internal-files/external-files and compile-debug are gone, the
environment variables INTERNAL=on/off and DEBUG=on/off replace them.

scripts/embed.py

@@ -1,22 +0,0 @@
-#!/usr/bin/python
-import shutil
-import sys
-from pathlib import Path
-
-external = ["false", "external", "no", "n"]
-
-with open("embed.go", "w") as f:
-    choice = ""
-    try:
-        choice = sys.argv[1]
-    except IndexError:
-        pass
-    folder = Path("embed")
-    if choice in external:
-        embed = False
-        shutil.copy(folder / "external.go", "embed.go")
-        print("Embedding disabled. \"data\" must be placed alongside the executable.")
-    else:
-        shutil.copy(folder / "internal.go", "embed.go")
-        print("Embedding enabled.")
-