Replace "Throwables.propagate(e); unreachableExitingStatement;" with equivalent "throw Throwables.propagate(e)."

CL automatically created by:
replace_string --pcre
(?m)^(\s*)(Throwables[.]propagate[(][^};]*[)];)\s*\b(?:throw|return)\b[^};]*;(?: *//[^\n]*)?
$1throw $2

I could make some additional improvements by removing the requirement that the next statement be a throw or return, but that would make changes that aren't necessarily safe, and indeed some are breakages.

Review by: gak@google.com