Truncates the primary and secondary identifiers. The resulting array has length
2 and contains the truncated primary and secondary identifiers.
Each identifier consists of components separated by "<".
The maximum length of the resulting
primaryIdentifier + "<<" secondaryIdentifier
primaryIdentifier - the original primary identifier
secondaryIdentifier - the original secondary identifier
length - the maximum length of the resulting identifier (including the "<<"
an array of length 2 containing the resulting identifier