Remove unnecessary textColor props from PicklistItem

[msmx-mnakagawa]

Summary

Just removed textColor='currentColor' prop from general icons in PicklistItem.

This is because it would be too much to apply it, as far as confirming references below.

References

• https://v1.lightningdesignsystem.com/components/menus/#Icon-on-the-Left
  Though this example is regarding Menus, general icons don't have .slds-current-color.
• https://v1.lightningdesignsystem.com/components/picklist/
  In the spec of Picklist, there is no example that has general icons.
• https://v1.lightningdesignsystem.com/components/picklist/#Open-Option-Selected
  In this Picklist example, though check mark icons are used, general icons aren't.
  At least, the check mark icons have .slds-current-color.

[reg-suit]

✨✨ That's perfect, there is no visual difference! ✨✨

Check out the report here.