IC: Small cleanup in KotlinClassInfo.kt

This is to address the not-yet-resolved comments in
https://github.com/JetBrains/kotlin/pull/5127, plus a few other small
(non-functional) changes.

^KT-58986: In progress

compiler/incremental-compilation-impl/testData/org/jetbrains/kotlin/incremental/classpathDiff/ClasspathSnapshotterTest/java/testSimpleClass/expected-snapshot/com/example/SimpleClass.json

@@ -12,7 +12,7 @@
     },
     "local": false
   },
-  "classAbiHash": -6381547343043280587,
+  "classAbiHash": 2881075740228300324,
   "classMemberLevelSnapshot": {
     "classAbiExcludingMembers": {
       "name": "com/example/SimpleClass",
@@ -21,17 +21,17 @@
     "fieldsAbi": [
       {
         "name": "publicField",
-        "abiHash": 8370167348140025367
+        "abiHash": -2698261112133196916
       }
     ],
     "methodsAbi": [
       {
         "name": "\u003cinit\u003e",
-        "abiHash": 9200648777950343158
+        "abiHash": 6894913661751208844
       },
       {
         "name": "publicMethod",
-        "abiHash": -2847179652577921235
+        "abiHash": -3018578973377534537
       }
     ]
   },