chore(scripts/test-versions): ensure tests are run against the correct files
chore(scripts/test-versions): ensure tests are run against the correct files

Previously, "version directories" (e.g. `./tmp/angular-1.4.10`) were considered "immutable", i.e.
if the directory existed, the files were not downloaded again. While this assumption holds for
released versions, it doesn't for the special `snapshot` version (which is the latest code from the
master branch and changes constantly).

Since it is not particularly costly, this commit removes the optimization altogether and always
downloads the files for each version.

Closes #8104

bluebirdtech/material,imjoeco/material,profoundry-us/material,hayloft/material,dmitriz/material,miguelcobain/material,crisbeto/material,miguelcobain/material,ilovett/material,HipsterZipster/material,DevVersion/material,bluebirdtech/material,DevVersion/material,daniel-nagy/material,crisbeto/material,ilovett/material,Splaktar/material,HarrisCorp/material,david-gang/material,dmitriz/material,imjoeco/material,clshortfuse/material,ErinCoughlan/material,david-gang/material,daniel-nagy/material,hodeyp/material,vertazzar/material,angular/material,HipsterZipster/material,imjoeco/material,pwistbac/material,david-gang/material,dmitriz/material,welkinhealth/material,colinskow/material,vertazzar/material,j3ski/material,hodeyp/material,pwistbac/material,angular/material,Splaktar/material,profoundry-us/material,ServiceManagementGroup/material,ErinCoughlan/material,welkinhealth/material,imjoeco/material,graingert/material,clshortfuse/material,SamDLT/material,gkalpak/material,bluebirdtech/material,ErinCoughlan/material,gkalpak/material,clshortfuse/material,oostmeijer/material,hayloft/material,Frank3K/material,HarrisCorp/material,marekmicek/material,j3ski/material,SamDLT/material,vertazzar/material,oostmeijer/material,gkalpak/material,welkinhealth/material,david-gang/material,Frank3K/material,colinskow/material,ServiceManagementGroup/material,HarrisCorp/material,programmist/material,programmist/material,HarrisCorp/material,welkinhealth/material,angular/material,colinskow/material,gkalpak/material,profoundry-us/material,Splaktar/material,ilovett/material,acoreyj/material,marekmicek/material,hayloft/material,hodeyp/material,Frank3K/material,graingert/material,epelc/material,marekmicek/material,DevVersion/material,pwistbac/material,graingert/material,hodeyp/material,epelc/material,crisbeto/material,programmist/material,miguelcobain/material,ServiceManagementGroup/material,ServiceManagementGroup/material,marekmicek/material,miguelcobain/material,HipsterZipster/material,vertazzar/material,ilovett/material,bluebirdtech/material,daniel-nagy/material,j3ski/material,clshortfuse/material,epelc/material,Splaktar/material,acoreyj/material,daniel-nagy/material,j3ski/material,HipsterZipster/material,acoreyj/material,acoreyj/material,SamDLT/material,epelc/material,graingert/material,hayloft/material,colinskow/material,profoundry-us/material,angular/material,ErinCoughlan/material,programmist/material,oostmeijer/material,pwistbac/material,DevVersion/material,oostmeijer/material,crisbeto/material,Frank3K/material,dmitriz/material,SamDLT/material