Dropped compatibility with composer/composer:<2.0.14

As discussed in #700
As noted in #700 (comment)

Since `composer/composer` broke BC in 2.0.14 by adding a runtime side-effect to a
functionally pure API (`InstalledVersions::getRawData()`) it is safest to move away
from it.

Since `composer-runtime-api:2.1.0` is not yet available, the safest approach is to
introduce a conflict with `composer/composer:<2.0.14` for now.

In the next release, we'll drop this `conflict` block and add bump `composer-runtime-api`
instead ( #702 ).

composer.json

@@ -25,6 +25,7 @@
         "webimpress/safe-writer":    "^2.2.0"
     },
     "conflict": {
+        "composer/composer":         "<2.0.14",
         "zendframework/zend-stdlib": "<3.2.1",
         "laminas/laminas-stdlib":    "<3.2.1",
         "doctrine/annotations":      "<1.6.1",

src/ProxyManager/Generator/Util/IdentifierSuffixer.php

@@ -6,7 +6,6 @@
 
 use Composer\InstalledVersions;
 
-use function is_callable;
 use function preg_match;
 use function serialize;
 use function sha1;
@@ -49,10 +48,6 @@ public static function getIdentifier(string $name): string
 
     private static function loadBaseHashSalt(): string
     {
-        return sha1(serialize(
-            is_callable([InstalledVersions::class, 'getAllRawData'])
-                ? InstalledVersions::getAllRawData() // Composer >= 2.0.14
-                : InstalledVersions::getRawData()
-        ));
+        return sha1(serialize(InstalledVersions::getAllRawData()));
     }
 }