fix github issue #200 - docs for 'strange object'

Fixes #200

The Guidebook claims that there's no symbol for 'S_strange_object'
which is literally true, but there is one for S_strange_obj.  It has
been in place longer than the paragraph claiming that there's no way
to customize that symbol.  I'm not sure why variant spelling was used.

Also, files.c doesn't use loadsyms[], it calls a routine which returns
a pointer to a specific element in that array.

doc/Guidebook.tex

@@ -45,7 +45,7 @@
 %.au
 \author{Original version - Eric S. Raymond\\
 (Edited and expanded for 3.6 by Mike Stephenson and others)}
-\date{May 7, 2019}
+\date{July 9, 2019}
 
 \maketitle
 
@@ -5048,17 +5048,6 @@ Default                      & Symbol Name                & Description\\
 \end{longtable}%
 }
 
-%.pg
-There is one additional class of object, described as ``strange object'',
-which will occasionally be the shape taken on by mimics and shown as
-`{\tt \verb+]+}'
-for maps displayed as text characters.
-Although the displayed character is the same as the default value for
-`S\verb+_+mimic\verb+_+def', it is a different symbol and there is no
-corresponding
-`S\verb+_+strange\verb+_+object' symbol nor any way to assign an
-alternate value for it.
-
 %.pg
 %.hn 2
 \subsection*{Configuring {\it NetHack\/} for Play by the Blind}