Remove Emacs 26 compatibility from Tramp

Remove Emacs 26 compatibility from Tramp

* doc/misc/tramp.texi (Remote processes): Don't mention Emacs version.
(Frequently Asked Questions): Adapt supported Emacs versions.

* doc/misc/trampver.texi:
* lisp/net/trampver.el: Change version to "2.7.0-pre".

* lisp/net/tramp-compat.el (tramp-compat-file-name-quoted-p)
(tramp-compat-file-name-quote, tramp-compat-file-name-unquote)
(tramp-compat-tramp-syntax, tramp-compat-exec-path)
(tramp-compat-time-equal-p, tramp-compat-flatten-tree)
(tramp-compat-progress-reporter-update)
(tramp-compat-ignore-error, tramp-compat-rx--transform-item)
(tramp-compat-rx--transform, tramp-compat-rx): Remove.

* lisp/net/tramp-adb.el:
* lisp/net/tramp-archive.el:
* lisp/net/tramp-cache.el:
* lisp/net/tramp-cmds.el:
* lisp/net/tramp-crypt.el:
* lisp/net/tramp-fuse.el:
* lisp/net/tramp-gvfs.el:
* lisp/net/tramp-integration.el:
* lisp/net/tramp-rclone.el:
* lisp/net/tramp-sh.el:
* lisp/net/tramp-smb.el:
* lisp/net/tramp-sshfs.el:
* lisp/net/tramp-sudoedit.el:
* lisp/net/tramp.el:
* lisp/net/trampver.el: Replace the removed `tramp-compat-*' items
by their real definition.  Don't use `tramp-compat-funcall' when
not needed.  Remove `with-no-warnings' and `ignore-errors' where
appropriate.

* lisp/net/tramp.el (tramp-file-name-for-operation): Rearrange list.
(tramp-handle-file-newer-than-file-p): Simplify.
(tramp-get-process-attributes): Don't check for existence of
`connection-local-criteria-for-default-directory'.
(tramp-handle-shell-command): Don't check for existence of
`shell-command-save-pos-or-erase', `async-shell-command-width' and
`shell-command-set-point-after-cmd'.
(tramp-handle-start-file-process): Call `make-process' directly.
(tramp-defined-time): New defsubst.
(tramp-get-local-gid): Don't check for existence of `group-name'.

* lisp/net/tramp-adb.el (tramp-adb-handle-set-file-times):
Use `tramp-defined-time'.
(tramp-adb-get-signal-strings): Don't bind `shell-file-name' and
`shell-command-switch'.

* lisp/net/tramp-archive.el (top, tramp-archive-file-name-handler):
Don't bind `max-specpdl-size' any longer.
(tramp-archive-autoload-file-name-regexp): Remove Emacs 26
specific code.
(top): Don't call `tramp-register-archive-autoload-file-name-handler'.

* lisp/net/tramp-gvfs.el (top): Don't bind `max-specpdl-size' any longer.
(tramp-gvfs-handle-set-file-times): Use `tramp-defined-time'.

* lisp/net/tramp-sh.el (tramp-sh-handle-set-file-times):
Use `tramp-defined-time'.

* test/lisp/net/tramp-archive-tests.el (tramp-archive--test-emacs27-p):
Remove.
(all):
* test/lisp/net/tramp-tests.el (all): Don't skip for Emacs 26.
Replace the removed `tramp-compat-*' items by their real
definition.  Don't use `tramp-compat-funcall' when not needed.
Remove `with-no-warnings' and `ignore-errors' where appropriate.
(with-connection-local-variables)
(shell-command-dont-erase-buffer): Don't declare.
(tramp-test10-write-region): Don't check for `make-empty-file'.
(tramp-test32-shell-command): Simplify.
(tramp-test34-explicit-shell-file-name): Don't protect
`explicit-shell-file-name' any longer.
(tramp--test-emacs27-p): Remove.