remove octree data

[tathey1]

• Replacing the ~1GB real data with small synthetic data
• Removing the precomputed uploaded data and generating it during test time
• Fixing tests to accomodate new data

In the future, it would be nice to generate the octree from scratch during test time.

[codecov[bot]]

Codecov Report

Merging #415 (4972167) into develop (c73e860) will increase coverage by 0.03%. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #415 +/- ## =========================================== + Coverage 78.81% 78.84% +0.03% =========================================== Files 25 25 Lines 4055 4061 +6 =========================================== + Hits 3196 3202 +6 Misses 859 859 ``` | [Impacted Files](https://app.codecov.io/gh/neurodata/brainlit/pull/415?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neurodata) | Coverage Δ | | |---|---|---| | [brainlit/utils/session.py](https://app.codecov.io/gh/neurodata/brainlit/pull/415?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=neurodata#diff-YnJhaW5saXQvdXRpbHMvc2Vzc2lvbi5weQ==) | `97.27% <100.00%> (+0.11%)` | :arrow_up: |