Revert "Use unique function ID for addCallback() and removeCallback()"
Revert "Use unique function ID for addCallback() and removeCallback()"

This reverts commit 4a59b3dcf0d74072e9819822cd7645c09f9f0425.

schriftgestalt/GlyphsSDK,schriftgestalt/GlyphsSDK,schriftgestalt/GlyphsSDK