Packaging Related Objects into an Extension

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/15/extend-extensions.html
Description:

This needs a section on how to remove Extensions.
My specific case is I have an old extension with no make file and i have to
remove it manually.
I have deleted all the files by looking at a sample make install log.
But even then something remains because pg_upgrade still flags a
c-extension that is already obsolete.