AK: Eradicate calls to warn().

Author: https://github.com/asynts
Commit: 1254cbbd0b
Pull-request: https://github.com/SerenityOS/serenity/pull/3848

Userland/env.cpp

@@ -58,7 +58,7 @@ int main(int argc, char** argv)
     String filepath = Core::find_executable_in_path(filename);
 
     if (filepath.is_null()) {
-        warn() << "no " << filename << " in path";
+        warnln("no {} in path", filename);
         return 1;
     }