Get rid of kitty's special OSC 52 protocol

A better solution from an ecosystem perspective is to just work with the
original protocol. I have modified kitty's escape parser to special case
OSC 52 handling without changing its max escape code size.

Basically, it works by splitting up OSC 52 escape codes longer than the
max size into a series of partial OSC 52 escape codes. These get
dispatched to the UI layer where it accumulates them upto the 8MB limit
and then sends to clipboard when the partial sequence ends.

See https://github.com/ranger/ranger/issues/1861

docs/clipboard.rst

@@ -1,29 +0,0 @@
-Pasting to clipboard
-=======================
-
-|kitty| implements the OSC 52 escape code protocol to get/set the clipboard
-contents (controlled via the :opt:`clipboard_control` setting). There is one
-difference in kitty's implementation compared to some other terminal emulators.
-|kitty| allows sending arbitrary amounts of text to the clipboard. It does so
-by modifying the protocol slightly. Successive OSC 52 escape codes to set the
-clipboard will concatenate, so::
-
-    <ESC>]52;c;<payload1><ESC>\
-    <ESC>]52;c;<payload2><ESC>\
-
-will result in the clipboard having the contents ``payload1 + payload2``. To
-send a new string to the clipboard send an OSC 52 sequence with an invalid payload
-first, for example::
-
-    <ESC>]52;c;!<ESC>\
-
-Here ``!`` is not valid base64 encoded text, so it clears the clipboard.
-Further, since it is invalid, it should be ignored by terminal emulators
-that do not support this extension, thereby making it safe to use, simply
-always send it before starting a new OSC 52 paste, even if you aren't chunking
-up large pastes, that way kitty won't concatenate your paste, and it will have
-no ill-effects in other terminal emulators.
-
-In case you're using software that can't be easily adapted to this
-protocol extension, it can be disabled by specifying ``no-append`` to the
-:opt:`clipboard_control` setting.