remove SPDX licenses (#71)

* remove license

* update manifest

MANIFEST.in

@@ -1,7 +1,6 @@
 include LICENSE
 include README.md
-
-recursive-include npe2 *.txt
+include CHANGELOG.md
 
 recursive-include tests *
 recursive-exclude * __pycache__

npe2/manifest/schema.py

@@ -4,7 +4,6 @@
 import re
 import sys
 from contextlib import contextmanager
-from enum import Enum
 from importlib import util
 from logging import getLogger
 from pathlib import Path
@@ -36,8 +35,6 @@
 if TYPE_CHECKING:
     from importlib.metadata import EntryPoint
 
-spdx_ids = (Path(__file__).parent / "spdx.txt").read_text().splitlines()
-SPDX = Enum("SPDX", {i.replace("-", "_"): i for i in spdx_ids})  # type: ignore
 
 logger = getLogger(__name__)
 
@@ -275,7 +272,6 @@ def from_file(cls, path: Union[Path, str]) -> PluginManifest:
         return mf
 
     class Config:
-        use_enum_values = True  # only needed for SPDX
         underscore_attrs_are_private = True
         extra = Extra.forbid