Replace dispatch table with simple if:elif:
Replace dispatch table with simple if:elif:

Changing to a tuple didn't did not solve the issue that RPython could not find a unique name for those function pointers. Now the traditional approach.
This also allows us to get rid of the exception for the HALT bytecode.

Signed-off-by: Stefan Marr <46f1a0bd5592a2f9244ca321b129902a06b53e03@stefan-marr.de>

SOM-st/PySOM,smarr/RTruffleSOM,smarr/PySOM,smarr/PySOM,smarr/RTruffleSOM,SOM-st/RTruffleSOM,SOM-st/RPySOM,SOM-st/PySOM,SOM-st/RTruffleSOM,SOM-st/RPySOM