delete examples for dev

[amudong]

delete examples for dev。
new examples path : https://github.com/dubbogo/dubbogo-samples

[codecov-io]

Codecov Report

Merging #228 into develop will decrease coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop     #228     +/-   ##
==========================================
- Coverage    64.69%   64.49%   -0.2%     
==========================================
  Files           95       95             
  Lines         6563     6563             
==========================================
- Hits          4246     4233     -13     
- Misses        1880     1892     +12     
- Partials       437      438      +1

Impacted Files	Coverage Δ
cluster/cluster_impl/base_cluster_invoker.go	54.71% <0%> (-16.99%)	⬇️
protocol/jsonrpc/server.go	59.79% <0%> (-1.51%)	⬇️
remoting/zookeeper/listener.go	46.9% <0%> (-1.04%)	⬇️
remoting/zookeeper/client.go	63.87% <0%> (-0.58%)	⬇️
registry/etcdv3/registry.go	51.51% <0%> (+1.01%)	⬆️
config_center/zookeeper/listener.go	86.95% <0%> (+4.34%)	⬆️

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