Revert "Identify data classes during extraction"

This reverts commit a61ba65c9f2182a578a7f4dbdb1c1657197f16cd, pending
adding a proper upgrade script for the DB change.

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -397,10 +397,6 @@ open class KotlinFileExtractor(
                     } else if (kind != ClassKind.CLASS && kind != ClassKind.OBJECT) {
                         logger.warnElement("Unrecognised class kind $kind", c)
                     }
-
-                    if (c.isData) {
-                        tw.writeKtDataClasses(classId)
-                    }
                 }
 
                 val locId = tw.getLocation(c)