Set up tests for postfix templates properly

If there are some other completion-like tests before these ones
it may lead to the situation when some value is already written by
`previouslySuggestedExpressions`, so it should be cleared in setUp

idea/tests/org/jetbrains/kotlin/idea/codeInsight/postfix/AbstractPostfixTemplateProviderTest.kt

@@ -28,6 +28,12 @@ abstract class AbstractPostfixTemplateProviderTest : KotlinLightCodeInsightFixtu
     override fun getProjectDescriptor() = KotlinWithJdkAndRuntimeLightProjectDescriptor.INSTANCE
     override fun getTestDataPath() = KotlinTestUtils.getHomeDirectory()
 
+
+    override fun setUp() {
+        super.setUp()
+        KtPostfixTemplateProvider.previouslySuggestedExpressions = emptyList()
+    }
+
     protected fun doTest(fileName: String) {
 
         myFixture.configureByFile(fileName)