Remove redundant dokkaHtml from build.gradle

The `build.gradle` contains two `dokkaHtmlPartial` configs
where the first one is redundant and apparently is overridden
by the second one.
The second one is correct any way.

* Remove the first `dokkaHtmlPartial` definition since it is
misleading and redundant

build.gradle

@@ -517,26 +517,6 @@ project('spring-integration-core') {
         testImplementation 'io.micrometer:micrometer-tracing-test'
     }
 
-    dokkaHtmlPartial {
-        outputDirectory.set(new File(buildDir, 'docs/kdoc'))
-        dokkaSourceSets {
-            main {
-                sourceRoots.setFrom(file('src/main/kotlin'))
-                classpath.from(sourceSets['main'].runtimeClasspath)
-                externalDocumentationLink {
-                    url.set(new URL("https://docs.spring.io/spring-integration/docs/$version/api/"))
-                    packageListUrl.set(file("$buildDir/api/element-list").toURI().toURL())
-                }
-                externalDocumentationLink {
-                    url.set(new URL('https://projectreactor.io/docs/core/release/api/'))
-                }
-                externalDocumentationLink {
-                    url.set(new URL('https://www.reactive-streams.org/reactive-streams-1.0.3-javadoc/'))
-                }
-            }
-        }
-    }
-
     dokkaHtmlPartial {
         outputDirectory.set(new File(buildDir, 'docs/kdoc'))
         dokkaSourceSets {