Why this "keybinding conflicts" message keeps appearing? How can I fix it?

After pressing M-x sly, I keep receiving this message:

[sly] SLIME detected in 'lisp-mode-hook', causes keybinding conflicts.Remove it for this Emacs session?

The odd thing is that SLIME is not installed in MELPA directories like the other packages:

~/.emacs.d/elpa$ ls -ltotal 28-rw-rw-r-- 1 pedro pedro  806 mai 26 16:42 0blayout-readme.txtdrwxrwxr-x 4 pedro pedro 4096 mai 14 17:17 archivesdrwx------ 3 pedro pedro 4096 mai 26 16:45 gnupgdrwxrwxr-x 2 pedro pedro 4096 mai 21 20:59 paredit-20191121.2328drwxrwxr-x 2 pedro pedro 4096 mai 14 17:27 rainbow-blocks-20210412.1937drwxr-xr-x 6 pedro pedro 4096 mai 22 21:02 sly-20210303.1148drwxrwxr-x 2 pedro pedro 4096 mai 22 21:18 transpose-frame-20200307.2119

Apparently, it was installed with QuickLisp. After pressing M-x locate-library in Emacs I get:

Library is file ~/.quicklisp/dists/quicklisp/software/slime-v2.26.1/slime.el

This is annoying me because Slime keybindings stopped working recently.

I am new to Common Lisp, Emacs, Sly/Slime, and Quicklisp. Maybe I messed up with stuff.