purge remnants of repo/categories.txt, which is long unused

tests/common.TestCase

@@ -2509,8 +2509,7 @@ class CommonTest(unittest.TestCase):
                 'repo/index.png',
                 'repo/index.xml',
             ]
-            non_repo_files = ['repo/categories.txt']
-            for f in repo_files + index_files + non_repo_files:
+            for f in repo_files + index_files:
                 open(f, 'w').close()
 
             repo_dirs = [
@@ -2543,10 +2542,6 @@ class CommonTest(unittest.TestCase):
                 self.assertTrue(os.path.exists(d), d + ' was created')
                 self.assertFalse(is_repo_file(d), d + ' not repo file')
 
-            for f in non_repo_files:
-                self.assertTrue(os.path.exists(f), f + ' was created')
-                self.assertFalse(is_repo_file(f), f + ' not repo file')
-
     def test_get_apksigner_smartcardoptions(self):
         os.chdir(self.tmpdir)
         with open('config.yml', 'w') as fp:

tests/repo/categories.txt

@@ -1,10 +0,0 @@
-1
-2.0
-Development
-GuardianProject
-Multimedia
-Phone & SMS
-Security
-System
-Time
-tests

tests/update.TestCase

@@ -22,6 +22,7 @@ import zipfile
 import textwrap
 from datetime import datetime
 from distutils.version import LooseVersion
+from pathlib import Path
 from testcommon import TmpCwd, mkdtemp
 from unittest import mock
 
@@ -1789,6 +1790,20 @@ class UpdateTest(unittest.TestCase):
                 "DEBUG:root:Checking archiving for org.smssecure.smssecure - apks:0, keepversions:6, archapks:0"
             ])
 
+    def test_categories_txt_is_removed_by_delete_unknown(self):
+        """categories.txt used to be a part of this system, now its nothing."""
+        os.chdir(self.testdir)
+        Path('config.yml').write_text('repo_pubkey: ffffffffffffffffffffffffffffffffffffffff')
+
+        categories_txt = Path('repo/categories.txt')
+        categories_txt.parent.mkdir()
+        categories_txt.write_text('placeholder')
+
+        self.assertTrue(categories_txt.exists())
+        with mock.patch('sys.argv', ['fdroid update', '--delete-unknown', '--nosign']):
+            fdroidserver.update.main()
+        self.assertFalse(categories_txt.exists())
+
 
 if __name__ == "__main__":
     os.chdir(os.path.dirname(__file__))