ENYO-470: Replace image asset references with sensible icon alternatives.

### Issue
The `InputHeaderSample` and `HeaderAutoCollapsingSample` both had numerous references to stale image assets for their `IconButton` controls.

### Fix
The stale references have been replaced with sensible icon substitutions.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>