RFR(XXS): 8214434: Disabling ZOptimizeLoadBarriers hits assert

[Nils Eliasson]

Hi,

This patch removes two asserts that was moved here with change "8208601: 
Introduce native oop barriers in C2 for OopHandle". These asserts are 
not correct when ZOptimizeLoadBarriers is disabled. The gvn.transform on 
the Proj-node may return a constant based on type analysis. When 
ZOptimizeLoadBarriers is enabled - the loadbarrier substitution will 
happen already at the call to gvn.transform(barrier), so the path with 
the asserts are not taken.

This code is going to change with a future patch of mine so choose just 
to remove them for now. I will consider adding a test or remove the flag 
in that change.

Bug: https://bugs.openjdk.java.net/browse/JDK-8214434

Webrev: http://cr.openjdk.java.net/~neliasso/8214434/webrev.02/

Regards,

Nils