Time: Remove serverside getter, and use atomic operations

It isn't possible to use atomic operations for floats, so don't use them there.

Having a lock is good out of other reasons too, because this way the float time
and the integer time both match, and can't get different values in a race,
e.g. when two setTimeofDay() get executed simultaneously.

src/server.h

@@ -223,7 +223,6 @@ public:
 	// Both setter and getter need no envlock,
 	// can be called freely from threads
 	void setTimeOfDay(u32 time);
-	inline u32 getTimeOfDay();
 
 	/*
 		Shall be called with the environment locked.