[PM-23019] Remove unused feature flag "item-share"

[djsmith85]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-23019

📔 Objective

Removes the unused feature flag "item-share" from server
Related to bitwarden/clients#15327

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[sonarqubecloud]

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

[github-actions]

Checkmarx One – Scan Summary & Details – 4f5f34b6-079c-42cc-b0ce-59e0cb515ff3

Great job, no security vulnerabilities found in this Pull Request

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.72%. Comparing base (74964bf) to head (01ebf6b).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6003   +/-   ##
=======================================
  Coverage   47.72%   47.72%           
=======================================
  Files        1692     1692           
  Lines       74972    74972           
  Branches     6758     6758           
=======================================
  Hits        35777    35777           
  Misses      37739    37739           
  Partials     1456     1456           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.