Remove synthetic flag from internal members

idea/testData/findUsages/kotlin/findFunctionUsages/kotlinInternalMethodUsages.0.kt

@@ -0,0 +1,12 @@
+// PSI_ELEMENT: org.jetbrains.kotlin.psi.JetNamedFunction
+// OPTIONS: usages
+package server
+
+public open class Server() {
+    open internal fun <caret>processRequest() = "foo"
+}
+
+public class ServerEx(): Server() {
+    override fun processRequest() = "foofoo"
+}
+

idea/testData/findUsages/kotlin/findFunctionUsages/kotlinInternalMethodUsages.1.kt

@@ -0,0 +1,8 @@
+import server.*;
+
+class Client {
+    public fun foo() {
+        Server().processRequest()
+        ServerEx().processRequest()
+    }
+}

idea/testData/findUsages/kotlin/findFunctionUsages/kotlinInternalMethodUsages.results.txt

@@ -0,0 +1,2 @@
+Function call (5: 18) Server().processRequest()
+Function call (6: 20) ServerEx().processRequest()