* In the VariableManager, we were not properly tracking if a file
had already been loaded, so we continuously append data to the end
of the list there for host and group vars, meaning large sets of data
are duplicated multiple times
* In the inventory, we were merging the host/group vars with the vars
local to the host needlessly, as the VariableManager already handles that.
This leads to needless duplication of the data and makes combining the
vars in VariableManager take even longer.
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