term--update-term-menu: Add the menu to term-terminal-menu

term--update-term-menu: Add the menu to term-terminal-menu

Reading bug#5641, the intention was to add this to the existing
"Terminal" menu for term-mode buffers, not to the local keymaps of all
other buffers.  Moreover, the existing code signaled errors when
switching to buffers with no local keymap, such as term-mode buffers
whose processes have died.

* lisp/term.el (term--update-term-menu): Add the menu to
term-terminal-menu, instead of implicitly trying to add it to every
local keymap.