[ISampleReader] Removed SetPTSDiff method

[CastagnaIT]

Description

after old PR #1907 SetPTSDiff method is no longer used since it is noop
since the mentioned PR at today no reports of subtitles malfunctions due to that code change
so lets remove this code

Motivation and context

cleanup

How has this been tested?

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• I have read the Contributing document
• My code follows the Code Guidelines of this project
• My change requires a change to the Wiki documentation
• I have updated the documentation accordingly

[kodiai]

Review Details

• Files reviewed: 2
• Lines changed: +0 -3
• Profile: strict (auto, lines changed: 3)
• Author: core (adapted tone)
• Findings: 0 critical, 0 major, 0 medium, 0 minor
• Review completed: 2026-02-16T13:41:04.552Z
• Keyword parsing:
  • ignored [isamplereader]
  • breaking change in body