move SkTextBox into utils

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/696293005
Cleanup: Remove SimpleiOSApp xcode project file.

There is already an GYP version for it in:
https://skia.googlesource.com/skia/+/master/gyp/SimpleiOSApp.gyp

BUG=None
TEST=None
R=caryclark@google.com

Review URL: https://codereview.chromium.org/691133004