Apply suggestions from code review

Author: baywet

src/main/java/com/microsoft/graph/core/Constants.java

@@ -17,10 +17,6 @@ private Constants() {
 	 * The content type for JSON responses
 	 */
 	public static final String JSON_CONTENT_TYPE = "application/json";
-	/**
-	 * The content type for text responses
-	 */
-	public static final String TEXT_CONTENT_TYPE = "text/plain";
 	/**
 	 * The binary content type header's value 
 	 */

src/main/java/com/microsoft/graph/http/CoreHttpProvider.java

@@ -422,7 +422,7 @@ public Request authenticateRequest(Request request) {
 
 				final String contentType = headers.get(Constants.CONTENT_TYPE_HEADER_NAME);
 				if (contentType != null && resultClass != InputStream.class && 
-							(contentType.contains(Constants.JSON_CONTENT_TYPE) || contentType.contains(Constants.TEXT_CONTENT_TYPE))) { // some services reply in text/plain with a JSON representation...
+							contentType.contains(Constants.JSON_CONTENT_TYPE)) {
 					logger.logDebug("Response json");
 					return handleJsonResponse(in, CoreHttpProvider.getResponseHeadersAsMapOfStringList(response), resultClass);
 				} else if (resultClass == InputStream.class) {