chore: remove old Emacs blueprint backup files (content.tex~, print.tex~, web.tex~)

[euprunin]

% git log blueprint/src/content.tex~ blueprint/src/print.tex~ blueprint/src/web.tex~
commit 78eafb1f6d8149d66d7a91ae7505b7350176f8cc
Author: Kevin Buzzard <[email protected]>
Date:   Sun Nov 19 18:52:13 2023 +0000

    add blueprint stuff

[kbuzzard]

Thanks!