Remove ChromePrerenderService, keeping only its skeleton behind.
ChromePrerenderService is no longer used, superseeded by (and partially
incompatible with) Custom Tabs. Remove the code, leaving only a skeleton
service behind, to prevent clients expecting it from having issues.
BUG=
621889
Committed:
https://crrev.com/a373e507aca138969f45b92619ab29b6eae73033
Cr-Commit-Position: refs/heads/master@{#401237}