Delete unused code to generate code (#1494)

FileLoader is not used! ClasspathLoader resolved .*pebble, so it's ok to
delete it.
Close #1480

Author: eucyt

generator/pom.xml

@@ -135,7 +135,7 @@
         <dependency>
             <groupId>io.pebbletemplates</groupId>
             <artifactId>pebble</artifactId>
-            <version>4.0.0</version>
+            <version>4.1.0</version>
         </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>

generator/src/main/java/line/bot/generator/pebble/PebbleTemplateAdapter.java

@@ -18,7 +18,6 @@ public class PebbleTemplateAdapter extends AbstractTemplatingEngineAdapter {
         .cacheActive(false)
         .newLineTrimming(false)
         .loader(new DelegatingLoader(Arrays.asList(
-            new FileLoader(),
             new ClasspathLoader()
         )))
         .autoEscaping(false)