How can I remove an alias, e.g. which was automatically created from merging rem with similar names?
You can directly delete the rem containing the alias (select and backspace):
All references will be renamed automatically to the original rem:
Note: There is a slighly misleading warning dialog similar to deleting normal rem. You can ignore it. It will not break any references.
Alternatively you can merge the alias rem (the one selected in the first picture) into the original rem or another alias (again).
Aliases are automatically removed if you rename/realias the last reference using them (but not by deleting it).