fix(php): remove stale PHP version fallbacks

[mrrobot47]

Summary

Mirrors the PHP version cleanup done in site-type-wp. The default is already PHP 8.4 here — PR #110 (php-fpm 8.5 support) correctly bumped the --php synopsis default: to 8.4, and EE injects that into the args before create() runs. This PR removes two leftovers from earlier defaults that were dead or actively wrong.

Changes

1. Drop the dead 'latest' fallback (PHP.php:201)

- $this->site_data['php_version'] = \EE\Utils\get_flag_value( $assoc_args, 'php', 'latest' );
+ $this->site_data['php_version'] = \EE\Utils\get_flag_value( $assoc_args, 'php' );

The synopsis default: 8.4 is always populated into $assoc_args['php'] before the command runs, so the 'latest' fallback never executed. It only served to confuse and drift from the real default — same dead code that was removed from site-type-wp.

2. Remove the stale 8.0 → 'latest' remap (PHP.php:251)

- $this->site_data['php_version'] = ( 8.0 === (double) $this->site_data['php_version'] ) ? 'latest' : $this->site_data['php_version'];

This dated back to when 8.0 was the latest image. With latest now resolving to easyengine/php8.4, the remap silently rewrote an explicit --php=8.0 request to 'latest' → the php8.4 image. Removing it ensures an explicitly requested version is always honoured. site-type-wp removed its equivalent line in the "Scrape latest in php version entry" change; this repo never got that cleanup.

Behaviour

Invocation	Before	After
(no --php)	8.4	8.4 (unchanged)
--php=latest	php8.4 image	php8.4 image (unchanged)
--php=8.0	silently → php8.4	php8.0 (fixed)

No change for the default or latest; the only behavioural difference is that --php=8.0 is now honoured instead of being rewritten.