Clean up more PGTK code

Clean up more PGTK code

* lisp/term/pgtk-win.el (featurep):
(pgtk):
(pgtk-use-im-context):
(pgtk-handle-nxopen):
(pgtk-handle-nxopentemp):
(pgtk-ignore-1-arg):
([C-drag-n-drop]):
([M-drag-n-drop]):
([C-M-drag-n-drop]):
(pgtk-alternate-modifier):
(pgtk-right-alternate-modifier):
(pgtk-right-command-modifier):
(pgtk-right-control-modifier):
(pgtk-do-hide-emacs):
(pgtk-hide-others):
(pgtk-do-hide-others):
(pgtk-emacs-info-panel):
(pgtk-do-emacs-info-panel):
(pgtk-next-frame):
(pgtk-prev-frame):
(after-make-frame-functions):
(tool-bar-mode):
(pgtk-toggle-toolbar):
(pgtk-print-buffer):
(scalable-fonts-allowed):
(pgtk-standard-fontset-spec):
(pgtk-store-cut-buffer-internal):
(pgtk-copy-including-secondary):
(pgtk-paste-secondary):
(pgtk-suspend-error):
(window-system-initialization):
(after-init-hook): Remove code mindlessly copied from ns-win.el,
delete unused custom group, write doc strings and rename
variables duplicated from X to their names on X.  Also reformat
comments and code.
(pgtk-use-im-context-handler): New function.

* src/pgtkfns.c (syms_of_pgtkfns): Delete useless
AppleScript (!) code copied from NS.
* src/pgtkselect.c: Write FIXME about selection API usage.

* src/pgtkterm.c (get_keysym_name): Implement correctly instead
of sprintf'ing the numeric value of the keysym into a static
buffer.
(pgtk_set_window_size):
(xg_scroll_callback): Delete code that was #if 0'd out and
doesn't make sense on PGTK.
(pgtk_delete_terminal): Remove misleading comment.