Remove the div kernel.

[advaitjain]

Manually confirmed that the Xtensa tests now pass with:

make -f tensorflow/lite/micro/tools/make/Makefile TARGET=xtensa OPTIMIZED_KERNEL_DIR=xtensa TARGET_ARCH=fusion_f1 XTENSA_CORE=F1_190305_swupgrade test -j8

Workaround for http://b/184059002

[google-ml-butler]

Thanks for contributing to TensorFlow Lite Micro.

To keep this process moving along, we'd like to make sure that you have completed the items on this list:

• Read the contributing guidelines for TensorFlow Lite Micro
• Created a TF Lite Micro Github issue
• Linked to the issue from the PR description

We would like to have a discussion on the Github issue first to determine the best path forward, and then proceed to the PR review.