The oldjava command was removed with bugid 4305613. There are still
a few references to the old behavior embedded various places.
Some known instances are:

src/share/bin/java.c
src/share/classes/sun/misc/Launcher.java
src/share/classes/sun/tools/java/ClassPath.java
src/share/classes/sun/tools/javac/BatchEnvironment.java
src/share/classes/com/sun/tools/javah/Main.java
src/share/javac/com/sun/tools/javac/v8/code/ClassReader.java

Most of these look at "sun.boot.class.path" and act in a particular
way if it is null (which would indicate that oldjava was run).

Bugid 4454990 deals with a similar issue in the hotspot workspace.