images: Remove references to N230

USRP N230 is no longer supported starting with UHD 4, and thus, we can
remove it from the image manifest. This will no longer download N230
images when calling uhd_images_downloader from UHD 4.


Original-commit: f1f6d8eac52bfecd840ace95c2d357641ae3b09c

tools/utils/image_package_mapping.py

@@ -265,13 +265,6 @@ PACKAGE_MAPPING = {
         'files': ["usrp_b200_fw.hex",
                   "usrp_b200_bl.img"],
     },
-    'n230': {
-        'type': 'n230',
-        'package_name': 'n230_n230_fpga_default-g{}.zip',
-        'files': ["usrp_n230_fpga.bin",
-                  "usrp_n230_fpga.bit",
-                  "usrp_n230_fpga.rpt"],
-    },
     'b100': {
         'type': 'usrp1',
         'package_name': 'usrp1_b100_fpga_default-g{}.zip',