histedit: remove redundant checks for unfinished histedit state
Both text-based and curses-based histedit already check for unfinished
operations (not just unfinished histedit), so there's no need to check
specifically for unfinished histedit.
Differential Revision: https://phab.mercurial-scm.org/D11508
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true