Fix incorrect color profiles in test images.

When running the rust-png test, libpng logs multiple warnings: libpng warning: iCCP: known incorrect sRGB profile Removing the color profiles fixes the warnings.
servo · larsbergstrom · May 7, 2014 · May 7, 2014 · May 7, 2014 · 7977b43f8771c7c93a1de6914896afadb6579f1c
commit 7977b43f8771c7c93a1de6914896afadb6579f1c
diff --git a/test/mozilla-dinosaur-head-logo.png b/test/mozilla-dinosaur-head-logo.png
diff --git a/test/rust-huge-logo.png b/test/rust-huge-logo.png
diff --git a/test/servo-screenshot.png b/test/servo-screenshot.png