[Spring] Remove unnecessary modifiers from API interface templates #954

Job	Run time
Build with JDK17 (samples/client/petstore/spring-http-interface-reactive-noResponseEntity)	1m 3s
Build with JDK17 (samples/openapi3/client/petstore/spring-cloud-3)	1m 33s
Build with JDK17 (samples/client/petstore/java-helidon-client/v3/mp/)	1m 11s
Build with JDK17 (samples/client/petstore/java/webclient-jakarta)	56s
Build with JDK17 (samples/client/petstore/spring-http-interface-noResponseEntity)	1m 13s
Build with JDK17 (samples/client/petstore/java/microprofile-rest-client-outer-enum)	1m 11s
Build with JDK17 (samples/server/petstore/java-helidon-server/v3/mp/)	1m 4s
Build with JDK17 (samples/server/petstore/java-camel/)	1m 14s
Build with JDK17 (samples/client/petstore/spring-http-interface)	1m 1s
Build with JDK17 (samples/client/petstore/spring-http-interface-reactive)	48s
Build with JDK17 (samples/server/petstore/java-helidon-server/v3/se)	1m 22s
Build with JDK17 (samples/openapi3/server/petstore/springboot-3)	1m 9s
Build with JDK17 (samples/client/petstore/java-helidon-client/v3/se)	58s
	14m 43s

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