move mzscheme' and mzlib/unit200' from core to "compatibility-lib"

Also, move `mzlib/sandbox' to "compatibility-lib".

original commit: 72c91629893290cce4ea4082b08449b1a6914738

pkgs/compatibility-pkgs/compatibility-lib/info.rkt

@@ -1,3 +1,5 @@
 #lang info
 (define collection 'multi)
-(define deps '("base" "net-lib"))
+(define deps '("base" 
+               "net-lib"
+               "sandbox-lib"))