[Utility] Refactor getVisitInstruments function

[jesscall]

Brief summary of changes

Comment in Utility Class

 * @note    Function comment written by Dave, not the author of this function.
 *       The return value format seems weird. Should possibly be refactored.
 * @note    Used in:
 *      - behavioural_qc/php/NDB_Form_behavioural_qc.class.inc
 *      - behavioural_qc/ajax/GetInstruments.php
 * @cleanup

I should mention that the files mentioned in the comment no longer exist and as far as I can tell there are no other uses of this function in the code base.

Testing instructions (if applicable)

1. Use the utility somewhere and make sure the output is in the form of an array: [$Test_name => $Full_name]

[jesscall]

Test_name_display is not in the test_battery table or schema

[jesscall]

@kongtiaowang can you help with the unit testing?

[driusan]

@jesscall can you rebase this to trigger the tests to run? I'm not sure why they're all stuck at "Expected"

[jesscall]

@driusan rebased!