cpu plugin: Remove temperature code for Mac OS X.

cpu plugin: Remove temperature code for Mac OS X.

This code would throw an error for some systems, because the temperature
couldn't be read. Since the plugin still works in general, this was very
confusing to users. Becaus the temperature, even when read sucessfully, was
never dispatched, remove the code entirely. We might want to add this back to
the apple_sensors plugin eventually.

Fixes: #22