remove $schema from JSON data/instance

	follow argumentation here json-schema/json-schema#220

	The reference to which JSON schema the JSON data belongs shall
be handled by the user, NOT from inside the data.

	Also the validation against a JSON schema, or the mapping from
data to schema shall be handled by the user.

	A convention (not determined by the json-schema) is that the
JSON schema has `$schema`, the JSON data not.

file-formats/intf/examples/z_aff_example_intf.intf.json

@@ -1,5 +1,4 @@
 {
-  "$schema": "://github.com/SAP/abap-file-formats/blob/main/file-formats/intf/intf.json",
   "version": "1",
   "header": {
     "description": "Example interface for ABAP file formats",

file-formats/intf/intf-v.1.json

@@ -6,11 +6,6 @@
   "description": "Interface properties",
   "type": "object",
   "properties": {
-    "$schema": {
-      "title": "Schema",
-      "description": "Format version",
-      "type": "string"
-    },
     "version": {
       "description": "The ABAP file format version for INTF.",
       "enum": [ "1" ]
@@ -304,7 +299,6 @@
   },
   "additionalProperties": false,
   "required": [
-    "$schema",
     "version",
     "header"
   ]

file-formats/intf/intf-v.2.json

@@ -6,11 +6,6 @@
   "description": "Interface properties",
   "type": "object",
   "properties": {
-    "$schema": {
-      "title": "Schema",
-      "description": "Format version",
-      "type": "string"
-    },
     "version": {
       "description": "The ABAP file format version for INTF.",
       "enum": [ "2" ]
@@ -304,7 +299,6 @@
   },
   "additionalProperties": false,
   "required": [
-    "$schema",
     "version",
     "header"
   ]