Tramp cleanup

Tramp cleanup

* lisp/net/tramp-sh.el (tramp-sh-extra-args): Remove compat code.
(tramp-sh-handle-make-symbolic-link): More robust check for
TARGET remoteness.

* lisp/net/tramp-smb.el (tramp-smb-handle-copy-directory):
Disable copying by tar temporarily, it doesn't work reliably.
(tramp-smb-do-file-attributes-with-stat): Resolve symlink.
(tramp-smb-handle-make-symbolic-link): Fix implementation.

* lisp/net/tramp.el (tramp-handle-file-symlink-p): Simplify.

* test/lisp/net/tramp-tests.el (tramp-test21-file-links):
Extend test.