Fix Coverity Scan issues in copy command

[troglobit]

Description

Address two issues identified by Coverity Scan:

1. CID 550484 (TOCTOU): Remove access() check before realpath()

   • realpath() already fails if file doesn't exist, making the access() check redundant and introducing a TOCTOU race
   • Simplifies code while improving security

2. CID 550483 (CHECKED_RETURN): Mark unchecked remove() calls

   • Add (void) cast to two remove() calls to explicitly indicate we don't care about the return value
   • These are cleanup operations for temp files where failure is acceptable, even expected

Checklist

Tick relevant boxes, this PR is-a or has-a:

• Bugfix
  • Regression tests
  • ChangeLog updates (for next release)
• Feature
  • YANG model change => revision updated?
  • Regression tests added?
  • ChangeLog updates (for next release)
  • Documentation added?
• Test changes
  • Checked in changed Readme.adoc (make test-spec)
  • Added new test to group Readme.adoc and yaml file
• Code style update (formatting, renaming)
• Refactoring (please detail in commit messages)
• Build related changes
• Documentation content changes
  • ChangeLog updated (for major changes)
• Other (please describe):

[mattiaswal]

👌