Remove .find_ignore files so that the Soong Finder searches the whole
tree again (needed for Bazel support)

Test: TH
Bug: b/188491905
Change-Id: I6df2cecebf3f82120bb90353aeb08f6b40cf30be
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2906252Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Geoff Lang <geofflang@chromium.org>