synapse guest module: move license files

Move them into the module folder so that they'll be properly included
in distribution builds, such as when installing this module via pip.

Also reword copyright headers to refer to the project root instead of
the repository root, which isn't included in distribution builds.

modules/restricted-guests/synapse/setup.cfg

@@ -6,8 +6,8 @@ long_description_content_type = text/markdown
 version = 1.0.0
 license = AGPL-3.0-only OR LicenseRef-Element-Commercial
 license_files =
-    ../../../LICENSE-AGPL-3.0
-    ../../../LICENSE-COMMERCIAL
+    LICENSE-AGPL-3.0
+    LICENSE-COMMERCIAL
 
 
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