ox-latex: Fix :options discrepancy between blocks and lists

* lisp/ox-latex.el (org-latex-plain-list): Do not automatically
  enclose value for :options attribute within square brackets.
  Instead, append them verbatim next to the block name, as special
  blocks do.
* doc/org.texi (@LaTeX{} specific attributes): Update manual.

doc/org.texi

@@ -11768,13 +11768,12 @@ the @LaTeX{} @code{\includegraphics} macro will be commented out.
 @cindex plain lists, in @LaTeX{} export
 
 Plain lists accept two optional attributes: @code{:environment} and
-@code{:options}.  The first one allows the use of a non-standard
-environment (e.g., @samp{inparaenum}).  The second one specifies
-optional arguments for that environment (square brackets may be
-omitted).
+@code{:options}.  The first one allows the use of a non-standard environment
+(e.g., @samp{inparaenum}).  The second one specifies additional arguments for
+that environment.
 
 @example
-#+ATTR_LATEX: :environment compactitem :options $\circ$
+#+ATTR_LATEX: :environment compactitem :options [$\circ$]
 - you need ``paralist'' package to reproduce this example.
 @end example
 

lisp/ox-latex.el

@@ -1877,18 +1877,13 @@ contextual information."
 	 (latex-type (let ((env (plist-get attr :environment)))
 		       (cond (env (format "%s" env))
 			     ((eq type 'ordered) "enumerate")
-			     ((eq type 'unordered) "itemize")
-			     ((eq type 'descriptive) "description")))))
+			     ((eq type 'descriptive) "description")
+			     (t "itemize")))))
     (org-latex--wrap-label
      plain-list
      (format "\\begin{%s}%s\n%s\\end{%s}"
 	     latex-type
-	     ;; Put optional arguments, if any inside square brackets
-	     ;; when necessary.
-	     (let ((options (format "%s" (or (plist-get attr :options) ""))))
-	       (cond ((equal options "") "")
-		     ((string-match "\\`\\[.*\\]\\'" options) options)
-		     (t (format "[%s]" options))))
+	     (or (plist-get attr :options) "")
 	     contents
 	     latex-type))))