Fix duplicate <opr> for sqrtss

Commit 88bb68bb46b754f6561b010d75dbf3b2d6fb3900 added avx instructions
but forgot to remove the old <opr> information for the sqrtss
instruction. Let's get rid of it.
tests: use bash instead of sh to run difftest.sh

On Ubuntu, /bin/sh is a symlink to /bin/dash, however difftest.sh uses
bash-specific constructs and fails when run using dash. Therefore, run
this script explicitly using bash.
Merge pull request #67 from vegard/avx

Fix duplicate <opr> for sqrtss
Merge pull request #68 from vegard/ubuntu

tests: use bash instead of sh to run difftest.sh