WebStart: Remove redundant unset() for $IP

WebStart: Remove redundant unset() for $IP

This seems redundant given it is unconditionally being set
two statements later. Probably a left-over from r36353 (c6b902f180),
which did an unset() because there was another variable called
$preIP, and the original would no longer be needed.

However, we currently only use one variable ($IP) and there's no
need to unset() it before setting.

Bug: T189966
Change-Id: I17d516709beabeb80bd72b37f70ac9b666a501d4
(cherry picked from commit 3aa0b0567ff64ecb74df7534c8812c78c323df7c)