Quick Fixes: Implement "Remove unused assignment" quickfix

#KT-9931 Fixed

idea/testData/quickfix/removeRedundantAssignment/constant.kt

@@ -0,0 +1,5 @@
+// "Remove redundant assignment" "true"
+fun test() {
+    var i: Int
+    <caret>i = 1
+}

idea/testData/quickfix/removeRedundantAssignment/constant.kt.after

@@ -0,0 +1,4 @@
+// "Remove redundant assignment" "true"
+fun test() {
+    var i: Int
+<caret>}

idea/testData/quickfix/removeRedundantAssignment/functionCall.kt

@@ -0,0 +1,7 @@
+// "Remove redundant assignment" "true"
+fun foo() = 1
+
+fun test() {
+    var i: Int
+    <caret>i = foo()
+}

idea/testData/quickfix/removeRedundantAssignment/functionCall.kt.after

@@ -0,0 +1,7 @@
+// "Remove redundant assignment" "true"
+fun foo() = 1
+
+fun test() {
+    var i: Int
+    <caret>foo()
+}

idea/testData/quickfix/removeRedundantAssignment/notRedundant.kt

@@ -0,0 +1,6 @@
+// "Remove redundant assignment" "false"
+fun foo(): Int {
+    var i = 1
+    <caret>i = 2
+    return i
+}

idea/testData/quickfix/removeRedundantAssignment/simpleRef.kt

@@ -0,0 +1,5 @@
+// "Remove redundant assignment" "true"
+fun test(n: Int) {
+    var i: Int
+    <caret>i = n
+}

idea/testData/quickfix/removeRedundantAssignment/simpleRef.kt.after

@@ -0,0 +1,4 @@
+// "Remove redundant assignment" "true"
+fun test(n: Int) {
+    var i: Int
+<caret>}