Drop Python 3.8 branches (#13776)

stdlib/_tracemalloc.pyi

@@ -1,4 +1,3 @@
-import sys
 from collections.abc import Sequence
 from tracemalloc import _FrameTuple, _TraceTuple
 
@@ -9,9 +8,6 @@ def get_traceback_limit() -> int: ...
 def get_traced_memory() -> tuple[int, int]: ...
 def get_tracemalloc_memory() -> int: ...
 def is_tracing() -> bool: ...
-
-if sys.version_info >= (3, 9):
-    def reset_peak() -> None: ...
-
+def reset_peak() -> None: ...
 def start(nframe: int = 1, /) -> None: ...
 def stop() -> None: ...