Remove backend tests on old inference

Also remove any mentions of NewInference, and rename some tests.

compiler/testData/codegen/box/functions/functionExpression/functionExpressionWithThisReference.kt

@@ -1,4 +1,3 @@
-
 fun Int.thisRef1() = fun () = this
 fun Int.thisRef2() = fun (): Int {return this}
 
@@ -31,4 +30,4 @@ fun box(): String {
     if ("bar".withLabel2() != "bar") return "Test 10 failed"
 
     return "OK"
-}
+}

compiler/testData/codegen/box/functions/functionExpression/functionExpressionWithThisReferenceNI.kt

@@ -1,36 +0,0 @@
-// !LANGUAGE: +NewInference
-// NewInference needed because of KT-26531
-
-fun Int.thisRef1() = fun () = this
-fun Int.thisRef2() = fun (): Int {return this}
-
-fun <T> T.genericThisRef1() = fun () = this
-fun <T> T.genericThisRef2() = fun (): T {return this}
-
-val Int.valThisRef1: () -> Int get() = fun () = this
-val Int.valThisRef2: () -> Int get() = fun (): Int {return this}
-
-val <T> T.valGenericThisRef1: ()->T get() = fun () = this
-val <T> T.valGenericThisRef2: ()->T get() = fun (): T {return this}
-
-val <T> T.withLabel1: ()->T get() = fun () = this@withLabel1
-val <T> T.withLabel2: ()->T get() = fun (): T {return this@withLabel2}
-
-fun box(): String {
-    if (1.thisRef1()() != 1) return "Test 1 failed"
-    if (2.thisRef2()() != 2) return "Test 2 failed"
-
-    if (3.genericThisRef1()() != 3) return "Test 3 failed"
-    if (4.genericThisRef2()() != 4) return "Test 4 failed"
-
-    if (5.valThisRef1() != 5) return "Test 5 failed"
-    if (6.valThisRef2() != 6) return "Test 6 failed"
-
-    if (7.valGenericThisRef1() != 7) return "Test 7 failed"
-    if (8.valGenericThisRef2() != 8) return "Test 8 failed"
-
-    if ("bar".withLabel1() != "bar") return "Test 9 failed"
-    if ("bar".withLabel2() != "bar") return "Test 10 failed"
-
-    return "OK"
-}