Revert "B::Deparse: loopexes have list prec"

Revert "B::Deparse: loopexes have list prec"

This reverts commit 6a31dbf44ee919c340a3372c95b28d581979d165.

It turns out to be wrong.  Loopexes do have low precedence, but not
as low as I thought.  Their precedence level is actually their own,
undocumented in perlop:

diff --git a/pod/perlop.pod b/pod/perlop.pod
index 3edeabd..c9a1adf 100644
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -49,6 +49,7 @@ values only, not array values.
     nonassoc   ..  ...
     right      ?:
     right      = += -= *= etc.
+    nonassoc   loop exits (last, next, goto)
     left       , =>
     nonassoc   list operators (rightward)
     right      not

I am reverting this for now, till we decide what it is that
needs fixing.