Remove unused symbol encoding

Remove unused symbol encoding
	* src/encoding.[Ch]
	(symbol_encoding, symbol_encoding_): remove (unused)

	* src/frontends/qt4/QLPainter.C
	(QLPainter::text): Remove commented code. It was used in pre
	unicode times to get unicode values of the symbol fonts if
	USE_UNICODE_FOR_SYMBOLS was defined, but this was never defined
	anyway, since the code points of the symbol fonts (as written in
	lib/symbols) are directly used.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15758 a592a061-630c-0410-9148-cb99ea01b6c8