Fix JacocoTaskExtension import error

Remove explicit import for JacocoTaskExtension as it's automatically available
when the jacoco plugin is applied, similar to how it's used in jfr-events module.

Author: trask

buildSrc/src/main/kotlin/otel.java-conventions.gradle.kts

@@ -1,6 +1,5 @@
 import io.opentelemetry.gradle.OtelJavaExtension
 import org.gradle.api.tasks.testing.logging.TestExceptionFormat
-import org.gradle.testing.jacoco.tasks.JacocoTaskExtension
 
 plugins {
   `java-library`