Revert "logging: Simple impl of multline pretty printing"

This reverts commit 31dfbb4.

Author: twmr

src/_pytest/logging.py

@@ -41,21 +41,6 @@ def __init__(self, terminalwriter, *args, **kwargs):
         if six.PY2:
             self._original_fmt = self._fmt
         else:
-
-            class PercentStyleMultiline(logging.PercentStyle):
-                def format(self, record):
-                    if "\n" in record.message:
-                        fmt = self._fmt
-                        dct = record.__dict__
-                        data_seq = [
-                            fmt % {**dct, "message": line}
-                            for line in record.message.splitlines()
-                        ]
-                        return "\n".join(data_seq)
-                    else:
-                        return self._fmt % record.__dict__
-
-            self._style = PercentStyleMultiline(self._style._fmt)
             self._original_fmt = self._style._fmt
         self._level_to_fmt_mapping = {}