sanitycheck: remove platform-level option

Since the move to YAML format and the change in how we define default
platforms this is no longer needed as we are able to set multiple
default platforms per architecture and not using a list based on
priority anymore.

Fixes #4445

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/scripts/sanitycheck b/scripts/sanitycheck
index 83b8f22..2be23b1 100755
--- a/scripts/sanitycheck
+++ b/scripts/sanitycheck
@@ -1427,7 +1427,6 @@
         tag_filter = args.tag
         exclude_tag = args.exclude_tag
         config_filter = args.config
-        platform_limit = args.platform_limit
         extra_args = args.extra_args
         all_plats = args.all
 
@@ -1685,7 +1684,7 @@
                                 instance_list))
                         self.add_instances(instances)
                     else:
-                        self.add_instances(instance_list[:platform_limit])
+                        self.add_instances(instance_list[:1])
 
                     for instance in list(
                             filter(lambda tc: not tc.platform.default, instance_list)):
@@ -1910,14 +1909,6 @@
         "as default in the platform metadata file will be chosen "
         "to build and test. ")
     parser.add_argument(
-        "-L", "--platform-limit", action="store", type=int, metavar="N",
-        default=1,
-        help="Controls what platforms are tested if --platform or "
-        "--all are not used. For each architecture specified by "
-        "--arch (defaults to all of them), choose the first "
-        "N platforms to test in the arch-specific .yaml file "
-        "'platforms' list. Defaults to 1.")
-    parser.add_argument(
         "-a", "--arch", action="append",
         help="Arch filter for testing. Takes precedence over --platform. "
         "If unspecified, test all arches. Multiple invocations "