Remove prebooting step
Remove prebooting step

Summary:
Prebooting step complicates script a bit and makes tests a bit longer.
Looks like tht with new xcode it is not needed anymore

Reviewed By: antiarchit

Differential Revision: D5103229

fbshipit-source-id: 49136f7164aa652f9539e5a32c9a5a09a5c4fe46

ymin/WebDriverAgent,ymin/WebDriverAgent,ymin/WebDriverAgent,ymin/WebDriverAgent