Minor cleanup.

Minor cleanup.
* term.el (term-send-raw, term-send-raw-meta): Use read-key-sequence's
key decoding rather than do it manually via last-input-event + ascii-character.
(term-exec): Use delete-and-extract-region.
(term-handle-ansi-terminal-messages): Remove unused var `end'.
(term-process-pager): Remove unused var `i'.
(term-dynamic-simple-complete): Make obsolete.
(serial-update-config-menu): Remove unused vars `y' and `str'.
(term-update-mode-line): Remove unused var `temp'.