RFR(T): 8225564: Remove wrong assert in clean_catch_blocks

[Nils Eliasson]

Hi,

This patch removes an assert that is wrong.

When traversing the graph for fixing the catch blocks, postorder is not 
guaranteed. The fix_up_uses can find a load that must be handled first. 
The cleanup already supports (and expects that).

Bug: https://bugs.openjdk.java.net/browse/JDK-8225564

Webrev: http://cr.openjdk.java.net/~neliasso/8225564/

Regards,

Nils