chore: remove redundant JUnit XML report configuration (#728)

The `junitXml.required`, `includeSystemOutLog` and `includeSystemErrLog`
properties all default to `true` in Gradle JUnitXmlReport, so setting
them explicitly was a no-op. The latter two are also @Incubating API

buildSrc/src/main/kotlin/mcp.multiplatform.gradle.kts

@@ -45,11 +45,6 @@ kotlin {
                 events("failed")
             }
             systemProperty("kotest.output.ansi", "true")
-            reports {
-                junitXml.required.set(true)
-                junitXml.includeSystemOutLog.set(true)
-                junitXml.includeSystemErrLog.set(true)
-            }
         }
     }
     macosArm64()