Stop tabix indexing Vep vcf file

Apparently the vcf output that vep produces isn't always sorted, so if
we want to keep this we'll have to sort the vcf first.
None of the other experts tabix index their vcfs, so if this expert
isn't run last the final vcf won't be tabix indexed anyways.
Various optimizations to improve Reporter performance
Do not keep around the uncompressed vcf file