You can edit image recipe and remove (comment out) line that should be located there:
IMAGE_INSTALL_append = “ chromium”
(it could be also in IMAGE_INSTALL += ), take a look here.
The image recipe file is bitbake file with the name that you use to build your image, you should be able to find it in some meta folder, e.g. meta-<>/meta-fsl-demos/recipes-fsl/images/fsl-image-gui-sdk.bb.
Note that IMAGE_INSTALL is not recommended when used in build directory conf/local.conf (and it looks it just doesn't work as far as I have seen). That is why the recommended way is to either modify existing image recipe or clone/modify it.