By all accounts it isn’t necessary there are several avast/windows10 topics in the forums.

Whilst I don’t have a win7 system that I feel is capable of running win10, so I won’t be installing it.

  • Acer Aspire One, Win7 Starter (32bit) 10.1", 1024X600 screen, 2GB DDR3 RAM, Intel Atom N255 (1.5GHz dual core) CPU and 250GB HDD.

The key I believe is that if an AV is win10 compatible then there shouldn’t be a need to uninstall it.