remove filtlong step, implement flye --asm-coverage

[kapsakcj]

--asm-coverage 100 should allow for flye to not be overwhelmed with too much data in the initial assembly process.

https://github.com/fenderglass/Flye/blob/flye/docs/USAGE.md#reduced-contig-assembly-coverage

[kapsakcj]

another potential solution is to use rasusa as a tool for RANDOMLY downsampling reads instead of filtlong. It's quite fast, much faster than filtlong, and is available in a docker or singularity container