Base: Clean up explicit uses of namespaces in places where they're not necessary.

This commit covers all of the common and base classes.

src/iosource/PktDumper.h

@@ -85,7 +85,7 @@ public:
 	 * @return True if succesful, false otherwise (in which case \a
 	 * Error() must have been called.)
 	 */
-	virtual bool Dump(const zeek::Packet* pkt) = 0;
+	virtual bool Dump(const Packet* pkt) = 0;
 
 protected:
 	friend class Manager;