Remove EncodedFile.writelines

This is implemented by IOBase already, which additionally checks if the
stream is not closed, and calls `write` per line.

Ref/via: pytest-dev#6558 (comment)

Author: blueyed

src/_pytest/capture.py

@@ -429,10 +429,6 @@ def write(self, obj):
             )
         return self.buffer.write(obj)
 
-    def writelines(self, linelist):
-        data = "".join(linelist)
-        self.write(data)
-
     @property
     def name(self):
         """Ensure that file.name is a string."""