remove trailing spaces from markdown files

[brodycj]

Platforms affected

Android

Motivation and Context

see title

Description

• remove trailing spaces from .github/ISSUE_TEMPLATE.md
• remove trailing spaces from .github/ISSUE_TEMPLATE/BUG_REPORT.md
• remove trailing spaces from .github/ISSUE_TEMPLATE/FEATURE_REQUEST.md
• remove trailing spaces from CONTRIBUTING.md

Testing

see below

Checklist

• I've run the tests to see all new and existing tests pass - on GitHub
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-commenter]

Codecov Report

Merging #995 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #995   +/-   ##
=======================================
  Coverage   68.11%   68.11%           
=======================================
  Files          21       21           
  Lines        1866     1866           
=======================================
  Hits         1271     1271           
  Misses        595      595           

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