Core/Misc: fixed warnings and building connection patcher with boost versions below 1.61

src/server/game/Entities/Unit/StatSystem.cpp

@@ -1016,7 +1016,6 @@ void Guardian::UpdateResistances(uint32 school)
 void Guardian::UpdateArmor()
 {
     float value = 0.0f;
-    float bonus_armor = 0.0f;
     UnitMods unitMod = UNIT_MOD_ARMOR;
 
     value  = GetModifierValue(unitMod, BASE_VALUE);