Rearrange symfile_bfd_open

Rearrange symfile_bfd_open

symfile_bfd_open handled what were remote files as a special case.
Converting from "remote:" files to "target:" made symfile_bfd_open
look like this:

  if remote:
    open bfd, check format, etc
    return
  local-specific stuff
  open bfd, check format, etc
  return

This commit rearranges symfile_bfd_open to remove the duplicated
code, like this:

  if local:
      local-specific stuff
  open bfd, check format, etc
  return

gdb/ChangeLog:

	* symfile.c (symfile_bfd_open): Reorder to remove duplicated
	checks and error messages.