docs: remove demo manifests required by website

[shashankram]

Description:
Removes the demo manifests required by the docs
website as these have been moved to the osm-docs
repo.

Affected area:

Functional Area
Other	[X]

Please answer the following questions with yes/no.

1. Does this change contain code from or inspired by another project? no

   • Did you notify the maintainers and provide attribution?

2. Is this a breaking change? no

[codecov-commenter]

Codecov Report

Merging #4455 (172f181) into main (bfc256d) will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #4455      +/-   ##
==========================================
- Coverage   69.21%   69.03%   -0.18%     
==========================================
  Files         212      212              
  Lines       14580    14580              
==========================================
- Hits        10091    10065      -26     
- Misses       4437     4463      +26     
  Partials       52       52              

Flag	Coverage Δ
unittests	69.03% <ø> (-0.18%)	⬇️

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

Impacted Files	Coverage Δ
pkg/crdconversion/crdconversion.go	57.46% <0.00%> (-17.17%)	⬇️
pkg/ticker/ticker.go	83.33% <0.00%> (-3.85%)	⬇️

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[jaellio]

In release_pull_request_template.md can the check "Updated the image tags used in the demo manifests" be removed?

[shashankram]

In release_pull_request_template.md can the check "Updated the image tags used in the demo manifests" be removed?

The words demo manifests here can be a bit misleading, where it could be referring to the automated demo manifests inlined in the bash scripts. I rephrased this.