Max Cutler

Uses PHP’s output buffering to buffer XML-RPC responses and strip superfluous whitespace.
Plugins, themes, and any other files executed during the WordPress load process can unintentionally emit whitespace, 
such as by including a newline character after an explicit closing “?>” PHP tag instead of letting PHP auto-close the 
file.

XML-RPC De-whitespacer

Removes leading and trailing whitespace from XML-RPC responses that can break some XML-RPC clients.

Amin Nazemi

Neatma

Protect your website from xmlrpc brute-force attacks,DOS and DDOS attacks, this plugin disables the XML-RPC and trackbacks-pingbacks on your WordPress website.
PLUGIN FEATURES 
(These are options you can enable or disable each one)
<ul>
<li>Disable access to xmlrpc.php file using .httacess file </li>
<li>Automatically change htaccess file permission to read-only (0444)</li>
<li>Disable X-pingback to minimize CPU usage </li>
<li>Disable selected methods from XML-RPC</li>
<li>Remove pingback-ping link from header</li>
<li>Disable trackbacks and pingbacks to avoid spammers and hackers</li>
<li>Rename XML-RPC slug to whatever you want</li>
<li>Black list IPs for XML-RPC</li>
<li>White list IPs for XML-RPC</li>
<li>Some options to speed-up your wordpress website</li>
<li>Disable JSON REST API</li>
<li>Hide WordPress Version</li>
<li>Disable built-in WordPress file editor</li>
<li>Disable wlw manifest</li>
<li>And some other options</li>
</ul>
What is XMLRPC
XML-RPC, or XML Remote Procedure Call is a protocol which uses XML to encode its calls and HTTP as a transport mechanism. 
Beginning in WordPress 3.5, XML-RPC is enabled by default. Additionally, the option to disable/enable XML-RPC was removed. For various reasons, site owners may wish to disable this functionality. This plugin provides an easy way to do so.
Why you should disable XML-RPC 
Xmlrpc has two main weaknesses
<ul>
<li>Brute force attacks: 
Attackers try to login to WordPress using xmlrpc.php with as many username/password combinations as they can enter. A method within xmlrpc.php allows the attacker to use a single command (system.multicall) to guess hundreds of passwords. Daniel Cid at Sucuri described it well in October 2015: “With only 3 or 4 HTTP requests, the attackers could try thousands of passwords, bypassing security tools that are designed to look and block brute force attempts.”</li>
<li>Denial of Service Attacks via Pingback: 
Back in 2013, attackers sent Pingback requests through xmlrpc.php of approximately 2500 WordPress sites to “herd (these sites) into a voluntary botnet,” according to Gur Schatz at Incapsula. “This gives any attacker a virtually limitless set of IP addresses to Distribute a Denial of Service attack across a network of over 100 million WordPress sites, without having to compromise them.”</li>
</ul>

Disable XML-RPC-API

The upgrade notice keeps coming back on every screen even after being dismissed. It looks very unprofessional to my clients and is embarrassing for me as a web developer, i would rather disable the plugin and use the code in a function. 

It should be permanently dismissible via a cookie, like for other plugins. It might be ok once, when the plugin is first installed or updated, but after that, it should never appear again. 

Good plugin, but upgrade nag is too annoying

A simple and lightweight plugin to disable XML-RPC API, X-Pingback and pingback-ping in WordPress 3.5+ for a faster and more secure website

XML-RPC De-whitespacer vs Disable XML-RPC-API