nvim: Remove quarto fn snippet

Removed `fn` snippet from quarto snippets since we already have the
functionally equivalent `]]` snippet for markdown (which quarto
extends).

nvim/.config/nvim/snippets/quarto.snippets

@@ -65,11 +65,6 @@ snippet eref Equation crossref
 snippet cite Citation
         [@${1:bib-key}]
 
-snippet fn Footnote
-        [^${1:id}]
-
-        [^${1}]: ${2:text}
-
 snippet shortcode Shortcode
         {{< $0 >}}