Move function `days_1950`to script `overlap_v6.py`

Only place where it is used. So we are reverting in part commit
68da90cd. We use again the function `days_1950` in script
`overlap_v6.py` since commit f46e1bc8.

Common/util_detect_eddies.py

-import datetime
-
-def days_1950(date_num):
-    """Convert Matlab serial date number to number of days since Jan 1st
-    1950.
-
-    """
-    date = datetime.date.fromordinal(date_num - 366) - datetime.date(1950, 1, 1)
-    return date.days
 
 def get_ishape(d_init, ishape_last, days_1950, eddy_index):
     k = days_1950 - d_init

Convert_Matlab/overlap_v6.py

@@ -10,7 +10,15 @@ import scipy.io as sio
 import csv
 import sys
 import json
-import convert_id
+import datetime
+
+def days_1950(date_num):
+    """Convert Matlab serial date number to number of days since Jan 1st
+    1950.
+
+    """
+    date = datetime.date.fromordinal(date_num - 366) - datetime.date(1950, 1, 1)
+    return date.days
 
 def adjust_n(n_Matlab):
     k_Matlab = (n_Matlab - 1) // e_overestim
@@ -27,7 +35,7 @@ n_dates = n_eddies.size
 print("n_dates =", n_dates)
 e_overestim = id_child.shape[0]
 print("e_overestim =", e_overestim)
-d_init = convert_id.days_1950(date_num[0])
+d_init = days_1950(date_num[0])
 
 with open("node_id_param.json", "w") as f:
     json.dump({"e_overestim": e_overestim, "d_init": d_init}, f)