[patch] remove docs for SSA_OP_VMAYUSE and other doc/tree-ssa.texi cleanups

[Aldy Hernandez <aldyh at redhat dot com>]

While debugging something completely unrelated I ran into this...

SSA_OP_VMAYUSE hasn't been around for a looong time.  For that matter, I 
think it was even me that got rid of it, so this was an sloppy oversight 
on my part.

I also noticed that the SSA_OP* definitions in the documentation have 
diverged from the source.  I'm not a big fan of source embedded in the 
documentation, but if we must, then at least let's put a `NOTE' in the 
source to keep the .texi file up to date.  I've done this.

I also cleaned up a small inconsistency in the comment preceding the 
macro definition of FOR_EACH_IMM_USE_STMT.

Tested on x86-64 Linux.

OK?

Attachment: curr
Description: Text document