Remove unused and overflowing function

Resolves https://github.com/owncloud/core/issues/10991 failure 4

lib/private/security/certificate.php

@@ -39,7 +39,6 @@ class Certificate implements ICertificate {
 			$info = openssl_x509_parse($data);
 			$this->commonName = isset($info['subject']['CN']) ? $info['subject']['CN'] : null;
 			$this->organization = isset($info['subject']['O']) ? $info['subject']['O'] : null;
-			$this->serial = $this->formatSerial($info['serialNumber']);
 			$this->issueDate = new \DateTime('@' . $info['validFrom_time_t'], $gmt);
 			$this->expireDate = new \DateTime('@' . $info['validTo_time_t'], $gmt);
 			$this->issuerName = isset($info['issuer']['CN']) ? $info['issuer']['CN'] : null;
@@ -49,17 +48,6 @@ class Certificate implements ICertificate {
 		}
 	}
 
-	/**
-	 * Format the numeric serial into AA:BB:CC hex format
-	 *
-	 * @param int $serial
-	 * @return string
-	 */
-	protected function formatSerial($serial) {
-		$hex = strtoupper(dechex($serial));
-		return trim(chunk_split($hex, 2, ':'), ':');
-	}
-
 	/**
 	 * @return string
 	 */
@@ -81,13 +69,6 @@ class Certificate implements ICertificate {
 		return $this->organization;
 	}
 
-	/**
-	 * @return string
-	 */
-	public function getSerial() {
-		return $this->serial;
-	}
-
 	/**
 	 * @return \DateTime
 	 */

lib/public/icertificate.php

@@ -24,11 +24,6 @@ interface ICertificate {
 	 */
 	public function getOrganization();
 
-	/**
-	 * @return string
-	 */
-	public function getSerial();
-
 	/**
 	 * @return \DateTime
 	 */

tests/lib/security/certificate.php

@@ -49,11 +49,6 @@ class CertificateTest extends \PHPUnit_Framework_TestCase {
 		$this->assertSame('Internet Widgits Pty Ltd', $this->invalidCertificate->getOrganization());
 	}
 
-	function testGetSerial() {
-		$this->assertSame('7F:FF:FF:FF:FF:FF:FF:FF', $this->goodCertificate->getSerial());
-		$this->assertSame('7F:FF:FF:FF:FF:FF:FF:FF', $this->invalidCertificate->getSerial());
-	}
-
 	function testGetIssueDate() {
 		$expected = new DateTime('2014-08-27 08:45:52 GMT');
 		$this->assertEquals($expected->getTimestamp(), $this->goodCertificate->getIssueDate()->getTimestamp());