refactor: Refactored variable names

Author: koreanMike513

src/main/java/com/f_lab/la_planete/domain/Food.java

@@ -49,10 +49,10 @@ public BigDecimal calculateCost(int quantity) {
     return price.multiply(BigDecimal.valueOf(quantity));
   }
 
-  public void minusQuantity(int deductions) {
-    if (totalQuantity - deductions < 0)
+  public void minusQuantity(int quantity) {
+    if (totalQuantity - quantity < 0)
       throw new IllegalStateException("수량이 부족합니다. 따라서 구매가 진행될 수 없습니다.");
 
-    totalQuantity -= deductions;
+    totalQuantity -= quantity;
   }
 }

src/main/java/com/f_lab/la_planete/domain/Voucher.java

@@ -36,7 +36,7 @@ public BigDecimal apply(BigDecimal totalCost, Currency currency) {
     if (ObjectUtils.isEmpty(currency))
       throw new IllegalStateException("화페 값이 비어있습니다. 적절히 변경 후 다시 시도해주시길 바랍니다.");
 
-    BigDecimal afterDiscounts = BigDecimal.ONE.subtract(discountRate);
-    return totalCost.multiply(afterDiscounts).setScale(currency.getRoundingScale(), currency.getRoundingMode());
+    BigDecimal multiplier = BigDecimal.ONE.subtract(discountRate);
+    return totalCost.multiply(multiplier).setScale(currency.getRoundingScale(), currency.getRoundingMode());
   }
 }