Remove wasted file read when loading package manifest

Filesystem get was introduced in #25012 as a locking mechanism to prevent partial reads of the manifest file.
In #26010 the locking was substituted by an atomic rename-based file write. The get called survived the refactor, resulting a noop file_get_contents that just trashes the output.

This commit removes the read entirely.
-
         return $this->manifest = file_exists($this->manifestPath) ?
             $this->files->getRequire($this->manifestPath) : [];
     }

src/Illuminate/Foundation/PackageManifest.php

@@ -106,8 +106,6 @@ protected function getManifest()
             $this->build();
         }
 
-        $this->files->get($this->manifestPath);
-
         return $this->manifest = file_exists($this->manifestPath) ?
             $this->files->getRequire($this->manifestPath) : [];
     }