remove redundant open() arg: encoding='utf8'

By default, open() returns a str:
https://docs.python.org/3/library/functions.html#open

By default, str is UTF-8:
https://docs.python.org/3/library/stdtypes.html#str

This used to matter on Python 2.x, but this code is 3.x only now.

fdroidserver/rewritemeta.py

@@ -34,7 +34,7 @@ def proper_format(app):
     s = io.StringIO()
     # TODO: currently reading entire file again, should reuse first
     # read in metadata.py
-    with open(app.metadatapath, 'r', encoding='utf8') as f:
+    with open(app.metadatapath, 'r') as f:
         cur_content = f.read()
     _ignored, extension = common.get_extension(app.metadatapath)
     if extension == 'yml':