I also use Explorer, and yes, my code is the same.
I usually just use Explorer, but I can and have used 7-Zip on occasion.
As I mentioned, it is in the "Open with" submenu.
But getting back to the original question, I don't know how to remove it.
I don't know if this is of any use, but it's from "Windows 7 Inside Out":
"You want to remove a program from the Recommended Programs section of
the Open With dialog box:
The contents of the Recommended Programs list are determined in part by
the registry key
(where filetype is the extension of the file type in question) . So, for
example, in the case shown in Figure 5-16*, the …\ .bmp\OpenWithList key
includes several values, one of which is Notepad .exe . Deleting the
unwanted item in the OpenWithList key removes it from the Recommended
Programs list . (Some items in the Recommended Programs and Open With
lists appear as the result of values within the HCR\ filetype key and
its subkeys . However, accidental additions to the lists, as described
in the preceding section, are always made in the HKCU hive)."
*This is the box which appears with the "Open with" program list in it
and the "Other programs" beneath it.