Rename SharedFile::parse -> SharedFile::parseRest.

Unlike ObjectFile or ArchiveFile, SharedFile had two parse functions,
parseSoName() and parse(). parse must have been called after parseSoName,
but that requirement was not obvious from their names. (So it looked
like you could call parse() on a shared object file right away.)

This patch rename parseRest. It is now obvious that there's no single
parse function for the shared object file.

llvm-svn: 256898