chore: bump required php version to 7.4 (#2838)

* chore: require min php 7.4

* Revert "feat: backport php 7.3 functions (#2803)"

This reverts commit 6df5a4bc14.

* [BandcampDaily] use array_key_first

* hard fail on php versions below 7.4

* update phpcompat linter

composer.json

@@ -22,7 +22,7 @@
         "rss": "https://github.com/RSS-Bridge/rss-bridge/commits/master.atom"
     },
     "require": {
-        "php": ">=7.1",
+        "php": ">=7.4",
         "ext-mbstring": "*",
         "ext-curl": "*",
         "ext-openssl": "*",