scons: Get rid of some unused cruft from Ruby/yacc.

These variables are never used, and so don't need to be set.

Change-Id: Ia345e3aa12b4437638943a436d28686b6e60acda
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40868
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>

SConstruct

@@ -425,10 +425,6 @@ if sanitizers:
         warning("Don't know how to enable %s sanitizer(s) for your "
                 "compiler." % sanitizers)
 
-# Set up common yacc/bison flags (needed for Ruby)
-main['YACCFLAGS'] = '-d'
-main['YACCHXXFILESUFFIX'] = '.hh'
-
 # Do this after we save setting back, or else we'll tack on an
 # extra 'qdo' every time we run scons.
 if main['BATCH']: