Completely switch over to _rtc variable

* Doing this will make it easier to shuffle the logic in WatchyRTC to
  these other subclasses of AbstractRTC
* I think we may even want to collapse WatchyRTC completely into
  AbstractRTC, as the two resemble each other pretty close. We will
  see what sort of design we end up with in the meantime

src/WatchyRTC.cpp

@@ -1,7 +1,6 @@
 #include "WatchyRTC.h"
 
-WatchyRTC::WatchyRTC()
-    : rtc_ds(false) {}
+WatchyRTC::WatchyRTC() {}
 
 // TODO: We can probably put all of this logic into AbstractRTC as a class
 // function. It would simplify this class even more, which would be nice

src/WatchyRTC.h

@@ -46,8 +46,6 @@ public:
 
 class WatchyRTC {
     public:
-        DS3232RTC rtc_ds;
-        Rtc_Pcf8563 rtc_pcf;
         uint8_t rtcType;
     public:
         WatchyRTC();