tutorial/java: Call bindService
tutorial/java: Call bindService

This fixes an inconsistency (caused by me) due to half-updating the docs
in commit 9368475.

bindService is not necessary when extending AbstractRouteGuide instead
of implementing RouteGuide. Using AbstractRouteGuide is becoming the
preferred method, but for now we just want fix the current method.

Fixes grpc/grpc-java#1850

wildebeestdev/grpc.github.io,wildebeestdev/grpc.github.io,avx2/avx2.github.io,wildebeestdev/grpc.github.io,avx2/avx2.github.io,avx2/avx2.github.io