Remove the completion command from under development command.

Author: afoucret

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/parser/GrammarInDevelopmentParsingTests.java

@@ -34,10 +34,6 @@ public void testDevelopmentRerank() {
         parse("row a = 1 | rerank \"foo\" on title with reranker", "rerank");
     }
 
-    public void testDevelopmentCompletion() {
-        parse("row a = 1 | completion concat(\"test\", \"a\") with inferenceId as fieldName", "completion");
-    }
-
     void parse(String query, String errorMessage) {
         ParsingException pe = expectThrows(ParsingException.class, () -> parser().createStatement(query));
         assertThat(pe.getMessage(), containsString("mismatched input '" + errorMessage + "'"));