Fix remnants of s32 enable_shaders

minetest.conf.example

@@ -166,10 +166,8 @@
 #trilinear_filter = false
 # Set to true to pre-generate all item visuals
 #preload_item_visuals = true
-# 0: disable shaders
-# (1: low level shaders; not implemented)
-# 2: enable high level shaders
-#enable_shaders = 2
+# Set to true to enable shaders. Disable them if video_driver = direct3d9/8.
+#enable_shaders = true
 # Set to true to enable textures bumpmapping. Requires shaders enabled.
 #enable_bumpmapping = false
 # The time in seconds it takes between repeated