gdb/contrib/dwarf-to-dwarf-assembler.py: remove unused imports

Remove imports reported as unused by flake8.

Change-Id: I1a1e5edab6ecd6ee774cb4bd20bf22b8952898aa
Approved-By: Tom Tromey <tom@tromey.com>

gdb/contrib/dwarf-to-dwarf-assembler.py

diff --git a/gdb/contrib/dwarf-to-dwarf-assembler.py b/gdb/contrib/dwarf-to-dwarf-assembler.py
index 60f2935..37bd1ba 100755
--- a/gdb/contrib/dwarf-to-dwarf-assembler.py
+++ b/gdb/contrib/dwarf-to-dwarf-assembler.py
@@ -43,8 +43,6 @@
 import re
 import sys
 from copy import copy
-from dataclasses import dataclass
-from datetime import datetime
 from functools import cache
 from io import BytesIO, IOBase
 from logging import getLogger