Reorganize codegen tests for old language versions

Put all files under a single "oldLanguageVersions" directory under test
data of each test

compiler/testData/codegen/box/operatorConventions/oldLanguageVersions/percentAsModOnBigIntegerWithoutRem.kt

@@ -1,11 +0,0 @@
-// !LANGUAGE: -ProhibitOperatorMod
-// !API_VERSION: 1.0
-// TARGET_BACKEND: JVM
-// FULL_JDK
-
-import java.math.BigInteger
-
-fun box(): String {
-    val m = BigInteger.valueOf(-2) % BigInteger.valueOf(3)
-    return if (m != BigInteger.valueOf(1)) "Fail: BigInteger(-2) mod BigInteger(3) == $m" else "OK"
-}