fix: remove content-length assertion for large file chunked downloads

Swoole's write() uses Transfer-Encoding: chunked which strips the
Content-Length header. The assertion was added by this PR but is
incorrect for the chunked download path used by large files.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/e2e/Services/Storage/StorageBase.php

@@ -867,7 +867,6 @@ trait StorageBase
         $this->assertEquals('attachment; filename="large-file.mp4"', $file7['headers']['content-disposition']);
         $this->assertEquals('video/mp4', $file7['headers']['content-type']);
         $this->assertEquals('bytes', $file7['headers']['accept-ranges']);
-        $this->assertNotEmpty($file7['headers']['content-length']);
         $this->assertNotEmpty($fileData);
         $this->assertEquals(md5_file(realpath(__DIR__ . '/../../../resources/disk-a/large-file.mp4')), md5($fileData)); // validate the file is downloaded correctly