removed extra extraneous comments

Cuts the multi-line rationale blocks down to what a reader of the file
needs. The reasoning behind the tagging setup belongs in the commit
messages that introduced it, not repeated above every \DocumentMetadata
block.

Also trims the README: drops the consequence clause explaining what
happens when the standard is declared without the tagging, drops the
quoted TeX Live 2024 error message, and notes that sid has a new enough
TeX Live for anyone not on Overleaf. Adds the caveat that a veraPDF
PASS is necessary but not sufficient, since a document whose body text
is all artifact passes too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

poster_template/main.tex

@@ -1,15 +1,6 @@
-% ACCESSIBILITY: this poster is not a tagged PDF. The beamer class
-% rejects \DocumentMetadata outright ("Class beamer Error: The beamer
-% class is not compatible with \DocumentMetadata"), and the LaTeX
-% Tagging Project lists both beamer and beamerposter as no-support,
-% meaning incompatible and not expected to change. beamerposter also
-% pulls in textpos and subfig, which are incompatible in their own
-% right.
-%
-% There is no way to make this template produce an accessible PDF
-% today. Rather than declare PDF/UA-2 and ship an untagged file, it
-% makes no claim at all. If a poster has to be accessible, supply a
-% tagged companion document built from the paper or memo template.
+% Not a tagged PDF: beamer rejects \DocumentMetadata, and the LaTeX
+% Tagging Project lists beamer and beamerposter as no-support. See the
+% Posters section of the README.
 \documentclass[xcolor=dvipsnames, 12pt]{beamer}
 
 \usepackage[size=custom, width=114, height=80, scale=1.5]{beamerposter}