Remove version restriction from Pillow in TVM codebase

[areusch]

@kparzysz-quic states: There are 3 security vulnerabilities in Pillow < 9.0.0. They are all considered critical.

CVE-2022-22815 2
CVE-2022-22816
CVE-2022-22817
apps/microtvm/ethosu/requirements.txt lists Pillow==8.3.2.

@areusch : note this was originally listed in the docs install script as a hard version limit, but it's since gone. i suspect the task here is to just remove it from the various places in the codebase which mention it.

https://github.com/apache/tvm/search?q=Pillow

[manupak]

cc : @grant-arm

[leandron]

Me and @grant-arm did some investigation in this and we found out that the fixed/safe versions of Pillow don't release for Python 3.6 anymore.

So this is one more reason for us to update our Docker images and CI, because this will certainly be trend that libraries stop releasing Python 3.6.