fix: removes unused constant

Signed-off-by: GitHub <[email protected]>

Author: baywet

src/Microsoft.OpenApi.OData.Reader/Common/Constants.cs

@@ -167,12 +167,6 @@ internal static class Constants
         /// </summary>
         public static string StringType = "string";
 
-        /// <summary>
-        /// integer type
-        /// </summary>
-        [Obsolete("integer is not a valid OpenAPI type. Use number instead.")]
-        public static string IntegerType = "integer";
-
         /// <summary>
         /// number type
         /// </summary>