[master] fix #9847

[wangchengming666]

fix #9847

翻了以前的一些issue 比如 #8212 和 #5122 都提到过这个问题，我认为这段强校验的代码没必要存在。

    if (actualTypeArgsLength != 2) {
        throw new IllegalArgumentException(MessageFormat.format(
                "[ServiceDefinitionBuilder] Map type [{0}] with unexpected amount of arguments [{1}]."
                        + Arrays.toString(actualTypeArgs), type, actualTypeArgs));
    }

虽然可以通过SPI来扩展，但是还是给用户带来了一定的困扰。

[codecov-commenter]

Codecov Report

Merging #9848 (f29433b) into master (1222676) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #9848      +/-   ##
============================================
+ Coverage     60.87%   60.89%   +0.02%     
+ Complexity      448      447       -1     
============================================
  Files          1100     1100              
  Lines         44560    44557       -3     
  Branches       6487     6486       -1     
============================================
+ Hits          27125    27135      +10     
+ Misses        14464    14456       -8     
+ Partials       2971     2966       -5     

Impacted Files	Coverage Δ
...bo/metadata/definition/builder/MapTypeBuilder.java	71.42% <ø> (+8.92%)	⬆️
...he/dubbo/remoting/transport/netty/NettyServer.java	70.17% <0.00%> (-3.51%)	⬇️
.../exchange/support/header/HeaderExchangeServer.java	67.61% <0.00%> (-1.91%)	⬇️
...ng/zookeeper/curator5/Curator5ZookeeperClient.java	51.97% <0.00%> (-1.13%)	⬇️
.../apache/dubbo/config/bootstrap/DubboBootstrap.java	54.62% <0.00%> (+0.15%)	⬆️
...apache/dubbo/common/extension/ExtensionLoader.java	80.41% <0.00%> (+0.41%)	⬆️
...etadata/report/support/AbstractMetadataReport.java	59.70% <0.00%> (+3.39%)	⬆️
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0.00%> (+4.34%)	⬆️
...ng/transport/dispatcher/all/AllChannelHandler.java	89.65% <0.00%> (+6.89%)	⬆️
...port/identifier/BaseServiceMetadataIdentifier.java	60.71% <0.00%> (+7.14%)	⬆️

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