Don't mark parameters of get/set/propertyDelegated functions as unused.

#KT-5974 fixed

compiler/testData/diagnostics/tests/regressions/Jet169.kt

@@ -1,4 +1,4 @@
-fun set(<!UNUSED_PARAMETER!>key<!> : String, <!UNUSED_PARAMETER!>value<!> : String) {
+fun set(key : String, value : String) {
   val a : String? = ""
   when (a) {
     "" -> <!DEBUG_INFO_SMARTCAST!>a<!>.get(0)

compiler/testData/diagnostics/tests/regressions/kt235.kt

@@ -35,13 +35,13 @@ fun main(args: Array<String>) {
 }
 
 class MyArray() {
-    fun get(<!UNUSED_PARAMETER!>i<!>: Int): Int = 1
-    fun set(<!UNUSED_PARAMETER!>i<!>: Int, <!UNUSED_PARAMETER!>value<!>: Int): Int = 1
+    fun get(i: Int): Int = 1
+    fun set(i: Int, value: Int): Int = 1
 }
 
 class MyArray1() {
-    fun get(<!UNUSED_PARAMETER!>i<!>: Int): Int = 1
-    fun set(<!UNUSED_PARAMETER!>i<!>: Int, <!UNUSED_PARAMETER!>value<!>: Int) {}
+    fun get(i: Int): Int = 1
+    fun set(i: Int, value: Int) {}
 }
 
 class MyNumber() {

compiler/testData/diagnostics/tests/regressions/kt258.kt

@@ -7,4 +7,4 @@ fun test() {
   attributes["href"] = "1" // inference fails, but it shouldn't
 }
 
-fun <K, V> MutableMap<K, V>.set(<!UNUSED_PARAMETER!>key<!> : K, <!UNUSED_PARAMETER!>value<!> : V) {}//= this.put(key, value)
+fun <K, V> MutableMap<K, V>.set(key : K, value : V) {}//= this.put(key, value)

compiler/testData/diagnostics/tests/regressions/kt459.kt

@@ -5,4 +5,4 @@ fun test() {
   attributes["href"] = "1" // inference fails, but it shouldn't
 }
 
-fun <K, V> Map<K, V>.set(<!UNUSED_PARAMETER!>key<!> : K, <!UNUSED_PARAMETER!>value<!> : V) {}//= this.put(key, value)
+fun <K, V> Map<K, V>.set(key : K, value : V) {}//= this.put(key, value)