Correct sensor amsua_n19 typo (NOAA-EMC#751)

The `Useflag check` in `amsua_n19.yaml` specified the wrong sensor. The
string `amaua_n19` was used instead of `amsua_n19`. The typo is
corrected in
[`feature/amsua_n19`](https://github.com/NOAA-EMC/GDASApp/tree/feature/amsua_n19).

Fixes NOAA-EMC#726

parm/atm/obs/config/amsua_n19.yaml

@@ -357,7 +357,7 @@ obs filters:
   - name: ObsFunction/ChannelUseflagCheckRad
     channels: *amsua_n19_channels
     options:
-      sensor: amaua_n19
+      sensor: amsua_n19
       channels: *amsua_n19_channels
       use_flag: [ 1,  1,  1,  1,  1,
                   1, -1, -1,  1,  1,