[ISSUE #9916] Remove getTimerCheckpoint() from BrokerController

[RongtongJin]

Which Issue(s) This PR Fixes

Fixes #9916

Brief Description

Remove getTimerCheckpoint() from BrokerController

How Did You Test This Change?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.69%. Comparing base (89e021e) to head (b63dfcd).

Files with missing lines	Patch %	Lines
...apache/rocketmq/broker/BrokerPreOnlineService.java	0.00%	5 Missing ⚠️
...apache/rocketmq/broker/slave/SlaveSynchronize.java	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #9905      +/-   ##
=============================================
- Coverage      49.78%   49.69%   -0.10%     
+ Complexity     12722    12697      -25     
=============================================
  Files           1314     1314              
  Lines          93928    93927       -1     
  Branches       12049    12049              
=============================================
- Hits           46763    46674      -89     
- Misses         41465    41540      +75     
- Partials        5700     5713      +13     

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