Revert "avoid intermediate copy from StringBuilder"

This reverts commit 59247ee.

Author: yuzawa-san

lib/sdk/server/src/main/java/com/launchdarkly/sdk/server/EvaluatorBucketing.java

@@ -7,10 +7,6 @@
 
 import org.apache.commons.codec.digest.DigestUtils;
 
-import java.nio.charset.StandardCharsets;
-import java.nio.CharBuffer;
-import java.security.MessageDigest;
-
 /**
  * Encapsulates the logic for percentage rollouts.
  */
@@ -63,9 +59,7 @@ static float computeBucketValue(
     }
 
     // turn the first 15 hex digits of this into a long
-    MessageDigest digest = DigestUtils.getSha1Digest();
-    digest.update(StandardCharsets.UTF_8.encode(CharBuffer.wrap(keyBuilder)));
-    byte[] hash = digest.digest();
+    byte[] hash = DigestUtils.sha1(keyBuilder.toString());
     long longVal = 0;
     for (int i = 0; i < 7; i++) {
       longVal <<= 8;