sys/console: Cosmetic name change
sys/console: Cosmetic name change

Global variable 'end' was renamed to 'trailing_chars' to avoid
name confusion.

Variable 'end' was passed to some functions and argument was also called end.
Same name 'end' was also used in few places as label for goto statement.

Global variable name was not revealing much of what it was used for nor was
its meaning explained by any comment.

Function insert_char was modifying global variable 'cur' while also using
local variable 'end' (which was defined in same line as cur) which could
cause some misunderstanding.

No functional changes to the code.

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core