optimize: remove use connPool.

[objcoding]

Ⅰ. Describe what this PR did

remove use connPool, Because apache object-pool is already used.

[codecov-io]

Codecov Report

Merging #2530 into develop will increase coverage by 0.12%.
The diff coverage is 12.50%.

@@              Coverage Diff              @@
##             develop    #2530      +/-   ##
=============================================
+ Coverage      50.94%   51.06%   +0.12%     
- Complexity      2763     2764       +1     
=============================================
  Files            551      550       -1     
  Lines          17569    17525      -44     
  Branches        2063     2064       +1     
=============================================
- Hits            8950     8949       -1     
+ Misses          7775     7735      -40     
+ Partials         844      841       -3     

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/io/seata/config/FileConfiguration.java	34.84% <0.00%> (-1.59%)	6.00 <0.00> (ø)
...ava/io/seata/core/rpc/netty/NettyClientConfig.java	45.31% <ø> (-1.66%)	22.00 <0.00> (-1.00)
...va/io/seata/core/rpc/netty/RpcClientBootstrap.java	42.25% <16.66%> (+8.54%)	6.00 <0.00> (ø)
...in/java/io/seata/server/session/GlobalSession.java	85.32% <0.00%> (+0.45%)	72.00% <0.00%> (+1.00%)
...o/seata/server/coordinator/DefaultCoordinator.java	55.00% <0.00%> (+0.50%)	29.00% <0.00%> (+1.00%)

[slievrly]

LGTM

[l81893521]

LGTM