Refine generic signature for Map.get/remove

Before this change generic signature wasn't written because of wrong
assumption about it absence in all cases where we replace generic parameter
with Object

compiler/testData/codegen/boxWithJava/collections/readOnlyMap/readOnlyMap.kt

@@ -0,0 +1,24 @@
+open class KMap<K, V> : Map<K, V> {
+    override val size: Int
+        get() = throw UnsupportedOperationException()
+
+    override fun isEmpty(): Boolean {
+        throw UnsupportedOperationException()
+    }
+
+    override fun containsKey(key: K) = true
+    override fun containsValue(value: V) = true
+
+    override fun get(key: K): V? {
+        throw UnsupportedOperationException()
+    }
+
+    override val keys: Set<K>
+        get() = throw UnsupportedOperationException()
+    override val values: Collection<V>
+        get() = throw UnsupportedOperationException()
+    override val entries: Set<Map.Entry<K, V>>
+        get() = throw UnsupportedOperationException()
+}
+
+fun box() = J.foo()