Hi,
the trash context menu entries (only) are in the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{645FF040-5081-101B-9F08-00AA002F954E}\shell
and
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{645FF040-5081-101B-9F08-00AA002F954E}\shellex\ContextMenuHandlers\
If you find the "avast" key, maybe you can delete it ... it should no longer appear in the trash menu but kept in the other windows contextual menus ?
Don't forget to backup your registry before deleting the key .... just in case
To bounce on what Dave says, in my case the Recycle Bin isn't treated in the same way as any other windows folder location ... see screenshot