Condafy fsl-sub

Hi @duncan, as you're aware, I'm porting all of FSL over to conda. I have created a mnt/conda branch on every FSL project, from which I am building conda packages. The mnt/conda branches contain minor tweaks to various projects, mostly to compilation flags. For fsl_sub, the only change is to remove the embedded conda recipe, as this will now be hosted at fsl/conda/fsl-sub>.

Please don't merge this just yet - I am intending that a mass mnt/conda merge across all projects will take place when everything is ready, hopefully within the couple of months.

You might note that I am also going to make a few CI related configuration changes to this repository, so that it uses the common CI rules that are hosted at fsl/fsl-ci-rules>. I've noticed that your jekyll branch has a .gitlab-ci.yml file. If/when you merge the jekyll branch into master, you can make a few simple changes to it to integrate it with the fsl-ci-rules, as outlined in the fsl-ci-rules README file.