Revert "Disallow missing events in UNTIL"

This reverts commit b63baef.

Author: luigidellaquila

x-pack/plugin/eql/src/main/java/org/elasticsearch/xpack/eql/parser/LogicalPlanBuilder.java

@@ -334,9 +334,6 @@ public Sequence visitSequence(SequenceContext ctx) {
                 throw new ParsingException(source, "A sequence requires a minimum of 2 queries (excluding UNTIL clause), found [1]");
             }
             until = queries.remove(queries.size() - 1);
-            if (until.isMissingEventFilter()) {
-                throw new ParsingException(source, "UNTIL clause cannot be a negative clause (missing event)");
-            }
         } else {
             until = defaultUntil(source);
         }

x-pack/plugin/eql/src/test/java/org/elasticsearch/xpack/eql/planner/QueryTranslatorFailTests.java

@@ -267,11 +267,6 @@ public void testSequenceWithTooLittleQueriesWithUntil() throws Exception {
         plan("sequence [any where true] [any where true] until [any where true]");
     }
 
-    public void testSequenceWithNegativeUntil() throws Exception {
-        String s = errorParsing("sequence [any where true] [any where true] until ![any where true]");
-        assertEquals("1:2: UNTIL clause cannot be a negative clause (missing event)", s);
-    }
-
     public void testSequenceWithIncorrectOption() throws Exception {
         EqlClientException e = expectThrows(EqlClientException.class, () -> plan("sequence [any where true] with repeat=123"));
         String msg = e.getMessage();