fix compiler warnings in test cases

tests/test_mission_planning.cpp

@@ -78,7 +78,6 @@ TEST_CASE("Angular position - circular orbit", "[mission][angular]") {
 }
 
 TEST_CASE("Phase angle calculation", "[mission][phase]") {
-    double earth_period = 365.25 * SECONDS_PER_DAY;
     double mars_period = 687.0 * SECONDS_PER_DAY;
     double transfer_time = 259.0 * SECONDS_PER_DAY;
 

tests/test_root_body_transitions.cpp

@@ -96,7 +96,6 @@ TEST_CASE("Root body round-trip - Earth -> Sun -> Mars -> Sun", "[root][round-tr
     const double TIME_STEP = 60.0;
     const double DAYS_TO_SIMULATE = 1000.0;
     const double SECONDS_PER_DAY = 86400.0;
-    const double AU = 1.496e11;
 
     SimulationState* sim = create_simulation(10, TIME_STEP);