Drop safety check from AssignmentPath.removeLast

In its last form it relied on prism object compare operation
that could be quite expensive. Moreover, the code is now clean enough
to make such safety check unnecessary.

This should fix some failing story tests.

A part of MID-6109 implementation.

model/model-impl/src/main/java/com/evolveum/midpoint/model/impl/lens/assignments/AssignmentPathImpl.java

@@ -62,8 +62,6 @@ void removeLast(AssignmentPathSegmentImpl segment) {
         AssignmentPathSegmentImpl last = last();
         if (last == null) {
             throw new IllegalStateException("Attempt to remove segment from empty path: " + this + "; segment=" + segment);
-        } else if (!last.equalsExceptForTarget(segment)) {
-            throw new IllegalStateException("Attempt to remove wrong segment from the end of path: " + this + "; segment=" + segment);
         } else {
             segments.remove(segments.size() - 1);
         }