obslog: correct help to state that obslog is the command name

Right now, `hg help obslog` says the following, which is a bit confusing:

```
hg olog [OPTION]... [[-r] REV]...

aliases: olog
```

Since the primary command name is determined by the order the commands are
defined in, and we use 'obslog' as the name for the pager, I've chosen
`hg obslog` as the canonical name and am only adjusting the help string.
8 jobs for topic/default/obslog-help-text in 5 minutes and 50 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
passed checks-py2 #170980

00:02:29

passed checks-py3 #170981

00:01:04

passed doc #170986

00:00:33

manual pytype #170979
allowed to fail manual
passed tests-py2-cext #170982

00:04:20

passed tests-py2-pure #170983

00:05:49

passed tests-py3-cext #170984

00:03:23

passed tests-py3-pure #170985

00:02:36