Removing all unsafe casts

- some of them are there to provide more definite type info
- and most of them to indicate the guarantee of a value being not null
There are removed because they should not be necessary, and will probably be removed from Graal entirely eventually

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

Conflicts:
	src/som/interpreter/nodes/ContextualNode.java
Let arguments in the arguments array

This reverts commit 206a24adef36169392856e9b504588d568a8d6be.
which was a revert of the original removal of this type-specialized arguments.

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