tweak-default: no longer enable the experimental return code

The change is quite new and undocumented (since it is experimental) so it seems
premature to make it available in tweak default. In addition, I am not sure the
new return code are frozen yet (eg: some of the initial feedback have not been
incorporated). Before the release I doubled check (probably with Martin) that
they were not enabled by default and got replied that they were only enabled in
the tests. Have I been aware that they have been also enabled in tweak default I
would I have lobbied to delay that.

I discovered they were in tweak default from users feedback. They found it an
unpleasant and unexpected surprise of 5.7.

So I suggest we no enable enable this experimental feature for Mercurial 5.7 and
revisit this later, when the feature will be more mature.

Differential Revision: https://phab.mercurial-scm.org/D9975

mercurial/ui.py

@@ -60,8 +60,6 b' urlreq = util.urlreq'
 # The config knobs that will be altered (if unset) by ui.tweakdefaults.
 tweakrc = b"""
 [ui]
-# Gives detailed exit codes for input/user errors, config errors, etc.
-detailed-exit-code = True
 # The rollback command is dangerous. As a rule, don't use it.
 rollback = False
 # Make `hg status` report copy information