Improve gdb_remote_download, remove gdb_download

Improve gdb_remote_download, remove gdb_download

This patch removes gdb_download in favor of gdb_remote_download, since
they are very close in functionality.  Also, in preparation for the
following patch about shared library handling during tests, it improves
gdb_remote_download so that it uses standard_output_file for any
destination board that is local, not only host.

If the destination board is remote, gdb_remote_download will use the
standard remote_download from DejaGnu, resulting in the file being
transferred on the remote system.

If the destination is local, gdb_remote_download will copy the file to
the standard test directory (found using standard_output_file).  Tcl's
file copy seems to handle gracefully cases where the source file is the
same as the destination, so I don't think it's necessary to check for
that case ourselves, as a previous version of the patch did.

I'd prefer to keep the name gdb_download instead of gdb_remote_download,
since I don't like the fact that gdb_remote_download implies that the
destination is remote, when it's not always the case.  However,
gdb_remote_download is used at many more places than gdb_download, so
it's easier to reuse that.  Also, since it's a wrapper around DejaGnu's
remote_download, it might be better to keep that name.  I don't know.

I ran the testsuite native, with native-gdbserver and with a
remote gdbserver, and didn't see any related failure.

gdb/testsuite/ChangeLog:

	* gdb.base/jit-so.exp: Use gdb_remote_download instead of
	gdb_download.  Use it even if the target is not remote.
	* gdb.base/jit.exp (compile_jit_test): Likewise.
	* lib/gdb.exp (gdb_remote_download): Copy files to the standard
	output directory if the destination board is local, otherwise use
	the standard remote_download from DejaGnu.
	(gdb_download): Remove.
	(gdb_load_shlibs): Use gdb_remote_download instead of
	gdb_download.
	* lib/gdbserver-support.exp (gdbserver_download_current_prog):
	Use gdb_remote_download instead of gdb_download.  Use it even if
	the target is not remote.
	* lib/mi-support.exp (mi_load_shlibs): Use gdb_remote_download
	instead of gdb_download.