Delete obsolete MANUAL section on compact and loose lists.

This gives a rule that has been been superseded by
commit 47537d26db.

The section is concerned to explain a discrepancy with
original Markdown.pl and its test suite.  In the case
under consideration, Markdown.pl gave strange results
which pandoc corrected.  I think it's no longer worth
wasting space on this, as its behavior seems clearly wrong.
If we are going to comment on every edge case with
Markdown.pl, the manual will get too long.

Babelmark 2 shows that some of the older implementations
follow Markdown.pl -- PHP Markdown, Python Markdown,
redcarpet, discount.

https://johnmacfarlane.net/babelmark2/?normalize=1&text=%2B+++First%0A%2B+++Second%0A++++-+a%0A++++-+b%0A%0A%2B+Third%0A

Closes #6684.

MANUAL.txt

@@ -3565,30 +3565,6 @@ list marker.  That is, example lists always behave as if the
 labels tend to be long, and indenting content to the
 first non-space character after the label would be awkward.
 
-### Compact and loose lists ###
-
-Pandoc behaves differently from `Markdown.pl` on some "edge
-cases" involving lists.  Consider this source:
-
-    +   First
-    +   Second:
-        -   Fee
-        -   Fie
-        -   Foe
-
-    +   Third
-
-Pandoc transforms this into a "compact list" (with no `<p>` tags around
-"First", "Second", or "Third"), while Markdown puts `<p>` tags around
-"Second" and "Third" (but not "First"), because of the blank space
-around "Third". Pandoc follows a simple rule: if the text is followed by
-a blank line, it is treated as a paragraph. Since "Second" is followed
-by a list, and not a blank line, it isn't treated as a paragraph. The
-fact that the list is followed by a blank line is irrelevant. (Note:
-Pandoc works this way even when the `markdown_strict` format is specified. This
-behavior is consistent with the official Markdown syntax description,
-even though it is different from that of `Markdown.pl`.)
-
 
 ### Ending a list ###