From systemd.unit(5):

Note that for drop-in files, if one wants to remove entries from a setting that is parsed as a list (and is
not a dependency), such as AssertPathExists= (or e.g. ExecStart= in service units), one needs to first
clear the list before re-adding all entries except the one that is to be removed. Dependencies (After=,
etc.) cannot be reset to an empty list, so dependencies can only be added in drop-ins. If you want to
remove dependencies, you have to override the entire unit.

https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html