Removed todo from main

Initially had thought using extern was unnecessary, but due to how ST's code is structured it may be necessary.

src/main.cpp

@@ -41,7 +41,7 @@
 // Select which board implementation to include based on cmake variable
 #ifdef BUILD_VARMINT_BOARD
 #include <Varmint.h>
-extern Varmint varmint; // TODO: Eliminate global variable
+extern Varmint varmint;
 #endif
 #ifndef BUILD_TEST_BOARD // Skip main function for gtest