fix(module:image): unsubscribe old src

[qugemingzizhenmafan]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #7102 (338f51c) into master (d9982e9) will increase coverage by 0.09%.
The diff coverage is 95.17%.

❗ Current head 338f51c differs from pull request most recent head 575d98a. Consider uploading reports for the commit 575d98a to get more accurate results

@@            Coverage Diff             @@
##           master    #7102      +/-   ##
==========================================
+ Coverage   89.63%   89.72%   +0.09%     
==========================================
  Files         488      488              
  Lines       15873    15937      +64     
  Branches     2584     2579       -5     
==========================================
+ Hits        14227    14299      +72     
+ Misses       1014     1006       -8     
  Partials      632      632              

Impacted Files	Coverage Δ
components/menu/submenu.component.ts	98.93% <ø> (-0.02%)	⬇️
components/popconfirm/popconfirm.ts	96.15% <ø> (ø)
components/time-picker/time-picker.component.ts	85.18% <ø> (ø)
components/carousel/carousel.component.ts	89.63% <88.23%> (+0.39%)	⬆️
components/switch/switch.component.ts	96.20% <90.00%> (+0.68%)	⬆️
components/cascader/cascader.component.ts	94.76% <94.44%> (+0.14%)	⬆️
components/date-picker/date-picker.component.ts	90.87% <100.00%> (-0.04%)	⬇️
...mponents/date-picker/date-range-popup.component.ts	91.35% <100.00%> (+1.35%)	⬆️
components/icon/icon.directive.ts	95.58% <100.00%> (+0.42%)	⬆️
components/image/image.directive.ts	91.13% <100.00%> (+0.47%)	⬆️
... and 10 more

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[hsuanxyz]

LGTM