[cleanup][admin] Remove unused methods in PersistentTopicsBase

[dao-jun]

Motivation

Since #15347 merged, PersistentTopicsBase#internalDeleteSubscriptionForcefully and PersistentTopicsBase#internalDeleteSubscriptionForNonPartitionedTopicForcefully are never used anywhere,
cleanup the codebase.

Modifications

1. Remove PersistentTopicsBase#internalDeleteSubscriptionForcefully
2. Remove PersistentTopicsBase#internalDeleteSubscriptionForNonPartitionedTopicForcefully

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[lhotari]

LGTM

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.77%. Comparing base (bbc6224) to head (25377eb).
Report is 118 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #22424      +/-   ##
============================================
+ Coverage     73.57%   73.77%   +0.19%     
+ Complexity    32624    32411     -213     
============================================
  Files          1877     1885       +8     
  Lines        139502   139814     +312     
  Branches      15299    15318      +19     
============================================
+ Hits         102638   103142     +504     
+ Misses        28908    28703     -205     
- Partials       7956     7969      +13     

Flag	Coverage Δ
inttests	26.98% <ø> (+2.40%)	⬆️
systests	24.49% <ø> (+0.16%)	⬆️
unittests	73.05% <ø> (+0.21%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...pulsar/broker/admin/impl/PersistentTopicsBase.java	69.20% <ø> (+3.74%)	⬆️

... and 186 files with indirect coverage changes