commit-tree: do not complete line in -F input

"git commit-tree -F <file>", unlike "cat <file> | git
commit-tree" (i.e. feeding the same contents from the standard
input), added a missing final newline when the input ended in an
incomplete line.

Correct this inconsistency by leaving the incomplete line as-is,
as erring on the side of not touching the input is preferrable
and expected for a plumbing command like "commit-tree".

Signed-off-by: Ross Kabus <rkabus@aerotech.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit-tree.c

@@ -102,7 +102,6 @@ int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 			if (fd && close(fd))
 				die_errno("git commit-tree: failed to close '%s'",
 					  argv[i]);
-			strbuf_complete_line(&buffer);
 			continue;
 		}