Updated note about supported PHP verrsions (#8613)

Author: jeff-matthews

src/_includes/install/php-versions-2.3.md

@@ -1,6 +1,4 @@
 Magento supports PHP 7.3.
 
 {:.bs-callout-warning}
-PHP 7.1 has reached [End of Life](https://www.php.net/supported-versions.php). To maintain PCI compliance, Magento should not be run on unsupported software.
-Installing from GitHub will no longer work with Magento 2.3.4/PHP 7.1.
-The only way to install 2.3.4 with PHP 7.1.x is with Composer.
+PHP 7.1 and 7.2 have reached [End of Life](https://www.php.net/supported-versions.php). To maintain PCI compliance, Magento should not be run on unsupported software. Magento 2.3.x supports PHP 7.3 only and has not been tested with PHP 7.1 or 7.2.