doc: Avoid use of formatting Texinfo macros (e.g., @code) inside @menu, @xref macros. * genpropdoc.m: Change @xref instances that pointed to XREFinterpreterusage to point to new node name. * octave.texi: Rename menu item "Use of the @code{interpreter} Property" to "Use of the "interpreter" Property". * plot.txi: Replace uses of @code macro within @node, @subsections by surrounding text with double quotes ("..."). Remove special @anchor macros that had been created to work around pointing directly to nodes with @code macro in them.