commit: drop uses of get_cached_commit_buffer()

The "--show-all" revision option shows UNINTERESTING commits. Some of these commits may be unparsed when we try to show them (since we may or may not need to walk their parents to fulfill the request). Commit 3131b71301 (Add "--show-all" revision walker flag for debugging, 2008-02-09) resolved this by just skipping pretty-printing for commits without their object contents cached, saying: Because we now end up listing commits we may not even have been parsed at all "show_log" and "show_commit" need to protect against commits that don't have a commit buffer entry. That was the easy fix to avoid the pretty-printer segfaulting, but: 1. It doesn't work for all formats. E.g., --oneline prints the oid for each such commit but not a trailing newline, leading to jumbled output. 2. It only affects some commits, depending on whether we happened to parse them or not (so if they were at the tip of an UNINTERESTING starting point, or if we happened to traverse over them, you'd see more data). 3. It unncessarily ties the decision to show the verbose header to whether the commit buffer was cached. That makes it harder to change the logic around caching (e.g., if we could traverse without actually loading the full commit objects). These days it's safe to feed such a commit to the pretty-print code. Since be5c9fb904 (logmsg_reencode: lazily load missing commit buffers, 2013-01-26), we'll load it on demand in such a case. So let's just always show the verbose headers. This does change the behavior of plumbing, but: a. The --show-all option was explicitly introduced as a debugging aid, and was never documented (and has rarely even been mentioned on the list by git devs). b. Avoiding the commits was already not deterministic due to (2) above. So the caller might have seen full headers for these commits anyway, and would need to be prepared for it. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>