perf(FrameBuffer.__next__()): change self.data in place

Author: deedy5

src/h2/frame_buffer.py

@@ -148,7 +148,7 @@ def __next__(self) -> Frame:
 
         # At this point, as we know we'll use or discard the entire frame, we
         # can update the data.
-        self.data = self.data[9+length:]
+        del self.data[:9+length]  # (self.data = self.data[9+length:])
 
         # Pass the frame through the header buffer.
         new_frame = self._update_header_buffer(f)