Update developer-guide.adoc

Typo: "created created" (twice)

Signed-off-by: Matthew Burgess <mattyb149@apache.org>

This closes #5168
diff --git a/nifi-docs/src/main/asciidoc/developer-guide.adoc b/nifi-docs/src/main/asciidoc/developer-guide.adoc
index 6152092..8dd6e81 100644
--- a/nifi-docs/src/main/asciidoc/developer-guide.adoc
+++ b/nifi-docs/src/main/asciidoc/developer-guide.adoc
@@ -1455,7 +1455,7 @@
 original FlowFile to the OutputStream for the new FlowFile.
 
 *Clone Method*
-If the content of the newly created created FlowFile is to be only a
+If the content of the newly created FlowFile is to be only a
 contiguous subset of the bytes of the original FlowFile, it is
 preferred
 to use the `clone(FlowFile, long, long)` method instead of the