Remove Unused Annotation.

[SteNicholas]

Motivation:

There are some unsed annotions in abstract class because it is unnecessary and its implements have their own annotation,for example @extension("http") in com.alipay.sofa.rpc.server.http.AbstractHttpServer

Modification:

Remove unsed annotions in abstract class.I have already checked 22 abstract class,only com.alipay.sofa.rpc.server.http.AbstractHttpServer has @extension annotion, so just remove this class annotion.

Result:

Fixes #192.

[codecov-io]

Codecov Report

Merging #193 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #193      +/-   ##
============================================
+ Coverage      71.2%   71.21%   +<.01%     
- Complexity      956      958       +2     
============================================
  Files           341      341              
  Lines         14213    14213              
  Branches       2286     2286              
============================================
+ Hits          10121    10122       +1     
- Misses         2897     2898       +1     
+ Partials       1195     1193       -2

Impacted Files	Coverage Δ	Complexity Δ
...lipay/sofa/rpc/server/http/AbstractHttpServer.java	71.02% <ø> (ø)	15 <0> (ø)	⬇️
...m/alipay/sofa/rpc/module/FaultToleranceModule.java	66.66% <0%> (-26.67%)	5% <0%> (ø)
.../alipay/sofa/rpc/registry/local/LocalRegistry.java	57.83% <0%> (+0.6%)	26% <0%> (+1%)	⬆️
...ava/com/alipay/sofa/rpc/config/RegistryConfig.java	90.19% <0%> (+0.98%)	0% <0%> (ø)	⬇️
.../sofa/rpc/bootstrap/DefaultClientProxyInvoker.java	88.7% <0%> (+1.61%)	0% <0%> (ø)	⬇️
.../main/java/com/alipay/sofa/rpc/tracer/Tracers.java	42.3% <0%> (+2.56%)	0% <0%> (ø)	⬇️

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