removed unused methods from derived module

More updates for the miniseed pipeline. The first purpose of this commit is renaming the "observatory" module "derived". This makes room for the observatory application(contains miniseed pipeline) that will take its place. The second purpose is housekeeping since the derived time series factory has been merged. Methods (delta f and rotate) previously calculated and wrote derived channels. Since they are no longer needed, they are removed from the derived module.

changed milestone to %Miniseed Webservice

requested review from @erigler

assigned to @pcain

added Needs Review label

added 4 commits

• 5e9db17f...7ee8e2b1 - 3 commits from branch ghsc/geomag:master
• 8413621e - removed unused methods from derived module

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added 1 commit

• 15655dd7 - removed unused methods from derived module

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mentioned in commit 62101770

merged

removed Needs Review label

changed milestone to %Miniseed Pipeline