Remove deprecated ExtensionComponentsFinder

[JohnNiang]

What type of PR is this?

/kind cleanup /area core /milestone 2.17.x

What this PR does / why we need it:

In https://github.com/halo-dev/halo/pull/5386, I marked ExtensionComponentsFinder as deprecated. Four months have passed, it's time to remove it.

Does this PR introduce a user-facing change?

移除过时 API **ExtensionComponentsFinder**。

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 70.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 57.06%. Comparing base (bc10336) to head (9d5c961). Report is 23 commits behind head on main.

Files	Patch %	Lines
...tension/service/impl/DefaultAttachmentService.java	41.66%	7 Missing :warning:
...pp/theme/dialect/GlobalHeadInjectionProcessor.java	77.77%	1 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6185 +/- ## ============================================ + Coverage 54.51% 57.06% +2.55% - Complexity 3523 3717 +194 ============================================ Files 646 651 +5 Lines 21862 22041 +179 Branches 1528 1542 +14 ============================================ + Hits 11917 12577 +660 + Misses 9328 8858 -470 + Partials 617 606 -11 ```

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[f2c-ci-robot[bot]]

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