Remove unused import in sample

Author: eleftherias

samples/boot/kotlin-webflux/src/main/kotlin/org/springframework/security/samples/config/SecurityConfig.kt

@@ -17,7 +17,6 @@
 package org.springframework.security.samples.config
 
 import org.springframework.context.annotation.Bean
-import org.springframework.security.config.Customizer
 import org.springframework.security.config.annotation.web.reactive.EnableWebFluxSecurity
 import org.springframework.security.config.web.server.ServerHttpSecurity
 import org.springframework.security.config.web.server.invoke