ESQL - remove some dead code (elastic#123720)

I was looking at some unrelated stuff in the Function Registry, and noticed this was never called.

Author: not-napoleon

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java

@@ -8,7 +8,6 @@
 package org.elasticsearch.xpack.esql.expression.function;
 
 import org.elasticsearch.Build;
-import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.util.CollectionUtils;
 import org.elasticsearch.common.util.FeatureFlag;
 import org.elasticsearch.xpack.esql.core.QlIllegalArgumentException;
@@ -163,12 +162,9 @@
 import java.util.Locale;
 import java.util.Map;
 import java.util.function.BiFunction;
-import java.util.regex.Pattern;
 import java.util.stream.Collectors;
 
-import static java.util.Collections.emptyList;
 import static java.util.Collections.unmodifiableList;
-import static java.util.stream.Collectors.toList;
 import static org.elasticsearch.xpack.esql.core.type.DataType.BOOLEAN;
 import static org.elasticsearch.xpack.esql.core.type.DataType.CARTESIAN_POINT;
 import static org.elasticsearch.xpack.esql.core.type.DataType.CARTESIAN_SHAPE;
@@ -269,16 +265,6 @@ public Collection<FunctionDefinition> listFunctions() {
         return defs.values();
     }
 
-    public Collection<FunctionDefinition> listFunctions(String pattern) {
-        // It is worth double checking if we need this copy. These are immutable anyway.
-        Pattern p = Strings.hasText(pattern) ? Pattern.compile(normalize(pattern)) : null;
-        return defs.entrySet()
-            .stream()
-            .filter(e -> p == null || p.matcher(e.getKey()).matches())
-            .map(e -> cloneDefinition(e.getKey(), e.getValue()))
-            .collect(toList());
-    }
-
     private static FunctionDefinition[][] functions() {
         return new FunctionDefinition[][] {
             // grouping functions
@@ -794,10 +780,6 @@ protected void buildDataTypesForStringLiteralConversion(FunctionDefinition[]...
         }
     }
 
-    protected FunctionDefinition cloneDefinition(String name, FunctionDefinition definition) {
-        return new FunctionDefinition(name, emptyList(), definition.clazz(), definition.builder());
-    }
-
     protected interface FunctionBuilder {
         Function build(Source source, List<Expression> children, Configuration cfg);
     }