Remove ivars from default Hardware::CPU methods

These methods are always overridden in the per-OS modules, so let's just
provide sensible defaults for documentation purposes.

Library/Homebrew/hardware.rb

@@ -8,19 +8,19 @@ class Hardware
     PPC_64BIT_ARCHS   = [:ppc64].freeze
 
     def type
-      @type || :dunno
+      :dunno
     end
 
     def family
-      @family || :dunno
+      :dunno
     end
 
     def cores
-      @cores || 1
+      1
     end
 
     def bits
-      @bits || 64
+      64
     end
 
     def is_32_bit?