Troponin-T uses value, should use valuenum

[alistairewj]

The cardiac marker concept grabs troponin-T:

mimic-code/mimic-iv/concepts/measurement/cardiac_marker.sql

Line 8 in 14b9f5f

, MAX(CASE WHEN itemid = 51003 THEN value ELSE NULL END) AS troponin_t

However almost every single value is ___ (due to the deidentification), so the derived table has all empty values. The valuenum column has the actual data however, so we should change the code to use valuenum instead.