Tools: Fix stateless handle issue

Fix the bug of removing elements from a list object while
enumerating this list object.
Refine variable names and comments to make it more readable.

Change-Id: Ibda2d0b538b1f900e6762d7346f1469ac3b7859f
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
Co-authored-by: Mingyang Sun <mingyang.sun@arm.com>