rtl.texi (sequence): Rewrite documentation to match the current use of SEQUENCE rtl...

rtl.texi (sequence): Rewrite documentation to match the current use of SEQUENCE rtl objects.

	* doc/rtl.texi (sequence): Rewrite documentation to match the
	current use of SEQUENCE rtl objects.
	* rtl.def (SEQUENCE): Likewise.

	* doc/rtl.texi (NOTE_INSN_EH_REGION_BEG, NOTE_INSN_EH_REGION_END):
	Update documentation.
	(NOTE_INSN_LOOP_BEG, NOTE_INSN_LOOP_END, NOTE_INSN_LOOP_CONT,
	NOTE_INSN_LOOP_VTOP): Remove documentation for non-existing notes.

	* reg-notes.def (REG_EH_CONTEXT): Remove unused note.

From-SVN: r197611