Fix mismatch between composer.lock and composer.json

The composer.lock file that was committed to the repository did not
match composer.json. It was built from a composer.json with an extra
section to override the PHP version check:

    "config": {
        "platform": {
            "php": "7.1.33"
        }
    }

Rebuild composer.lock without that config section, to prevent warnings
from Composer due to the mismatch.

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "f5bf19931f73cc09d7a4ce127b75b30e",
+    "content-hash": "10ace42afd0f39a29a7e847743677137",
     "packages": [
         {
             "name": "gettext/gettext",
@@ -7003,8 +7003,5 @@
     "platform-dev": {
         "ext-curl": "*"
     },
-    "platform-overrides": {
-        "php": "7.1.33"
-    },
     "plugin-api-version": "1.1.0"
 }