Fix creation of duplicate runtimeClasspath configuration

```
An exception occurred applying plugin request [id: 'org.jetbrains.kotlin.jvm']
> Failed to apply plugin class 'org.gradle.api.plugins.JavaPlugin'.
   > Could not create domain object 'java' (JvmSoftwareComponentInternal) in SoftwareComponent container
      > Cannot add a configuration with name 'runtimeClasspath' as a configuration with that name already exists.
```

Author: lauzadis

build-plugins/smithy-build/src/main/kotlin/aws/sdk/kotlin/gradle/codegen/SmithyBuildPlugin.kt

@@ -95,7 +95,6 @@ class SmithyBuildPlugin : Plugin<Project> {
         listOf(
             "smithyCli",
             "smithyBuild",
-            "runtimeClasspath",
         ).map(configurations::maybeCreate)
 
         tasks.register<SmithyBuildTask>(TASK_GENERATE_SMITHY_PROJECTIONS) {