remove ECMWF_old + add more comments

+ remove the unused [ECMWF_old]
+ add more comments on [CDS] and [ECMWF] for clearance.

pyaps3/model.cfg

@@ -1,20 +1,17 @@
 # vim: set filetype=cfg:
 #####key for ECMWF in Climate Data Store Application Program Interface
 #Get it from https://retostauffer.org/code/Download-ERA5/
+#for ERA5
 [CDS]
 key = your-uid:your-api-key
 
-#The key to the new server for ECMWF
-##Get it from https://software.ecmwf.int/wiki/display/WEBAPI/Accessing+ECMWF+data+servers+in+batch 
+#####The key to the new server for ECMWF
+#Get it from https://software.ecmwf.int/wiki/display/WEBAPI/Accessing+ECMWF+data+servers+in+batch 
+#for ERA-Interim [outdated]
 [ECMWF]
 email = the-email-address-used-as-login@ecmwf-website.org
 key = 
 
-#####Passwd and key for download from ecmwf.int. Old version.
-[ECMWF_old]
-email = the-email-adress-used-as-login@ecmwf-website.org
-key = 
-
 #####Passwd and key for download from ucar
 [ERA]
 email = the-email-adress-used-as-login@ucar-website.org