Clean up old float.h in incremental build dirs after libc++ roll

Bug: 503250165
Change-Id: Ic5b8991b07fc8c160047cb83380cc024e0498266
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7794599
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1620702}
NOKEYCHECK=True
GitOrigin-RevId: 0a4735880df6637c27ee5a2581d31288b365141c