Remove template engine after upgrading theme

[JohnNiang]

What type of PR is this?

/kind bug
/area core
/milestone 2.20.x

What this PR does / why we need it:

This PR removes template engine instead of clearing cache of template engine after upgrading theme to resolve incomplete cache clear.

Which issue(s) this PR fixes:

Fixes #7056

Special notes for your reviewer:

1. Try to install the theme theme-earth 1.12.0
2. Request index page and you will see the 上一页 which should be 下一页
3. Try to upgrade to the theme theme-earth 1.12.1
4. Request index page and you should see the 下一页 directly.

Does this PR introduce a user-facing change?

修复升级主题后语言包未更新的问题

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 57.26%. Comparing base (eff73dc) to head (2098964).
Report is 54 commits behind head on main.

Files with missing lines	Patch %	Lines
...java/run/halo/app/theme/TemplateEngineManager.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7057      +/-   ##
============================================
+ Coverage     56.99%   57.26%   +0.26%     
- Complexity     3999     4010      +11     
============================================
  Files           714      712       -2     
  Lines         24110    24144      +34     
  Branches       1585     1592       +7     
============================================
+ Hits          13742    13826      +84     
+ Misses         9756     9704      -52     
- Partials        612      614       +2     

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[ruibaby]

/lgtm

[guqing]

/approve

[f2c-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: guqing

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