I have created multiple Conda envs which I use as IPython kernels in Hydrogen for Atom using the following suggestion:
source activate thisenv
python -m ipykernel install --user --name thisenv
After deleting such a Conda env, however, Atom-Hydrogen still gives me that kernel as an option to select from when compiling the code.
How does one unlink or remove a Conda env after it is linked as a kernel to Atom-Hydrogen?
The original command you ran was to register your env as a kernel, which on OS X results in creating a folder in a common area, like so
/Users/<user>/Library/Jupyter/kernels/thisenv
If you only want to deregister the environment (but not delete it), you can simply delete the thisenv folder from this directory (or wherever the equivalent folder is on other systems). It is not necessary to remove the environment from Conda.
If you're having trouble finding where the env is registered, you can use the kernelspecs package to locate all the available kernels. This is the package that Atom uses to find kernels.