Replace System.getProperties().remove(x) with System.clearProperty(x)

This commit migrates to the not-so-new System.clearProperty() method
introduced in Java 1.5.

spring-context/src/test/java/org/springframework/context/config/ContextNamespaceHandlerTests.java

@@ -43,7 +43,7 @@ class ContextNamespaceHandlerTests {
 
 	@AfterEach
 	void tearDown() {
-		System.getProperties().remove("foo");
+		System.clearProperty("foo");
 	}
 
 

spring-context/src/test/java/org/springframework/context/expression/ApplicationContextExpressionTests.java

@@ -196,7 +196,7 @@ class ApplicationContextExpressionTests {
 			assertThat(tb6.tb).isSameAs(tb0);
 		}
 		finally {
-			System.getProperties().remove("country");
+			System.clearProperty("country");
 		}
 	}
 
@@ -230,8 +230,8 @@ class ApplicationContextExpressionTests {
 			assertThat(tb.getCountry2()).isEqualTo("-UK2-");
 		}
 		finally {
-			System.getProperties().remove("name");
-			System.getProperties().remove("country");
+			System.clearProperty("name");
+			System.clearProperty("country");
 		}
 	}
 
@@ -264,7 +264,7 @@ class ApplicationContextExpressionTests {
 			assertThat(FileCopyUtils.copyToString(resourceInjectionBean.reader)).isEqualTo(FileCopyUtils.copyToString(new EncodedResource(resource).getReader()));
 		}
 		finally {
-			System.getProperties().remove("logfile");
+			System.clearProperty("logfile");
 		}
 	}