share: remove unexpected heading from "verbose" container in help test

`test-gendoc-*.t` have been failing for me since 91425656e2b1 (share:
add documentation about share-safe mode in `hg help -e share`,
2020-11-27) with this kind of output:

```
    --- /usr/local/google/home/martinvonz/hg/tests/test-gendoc-ru.t
    +++ /usr/local/google/home/martinvonz/hg/tests/test-gendoc-ru.t.err
    @@ -2,3 +2,9 @@

       $ $TESTDIR/check-gendoc ru
       checking for parse errors
    +  gendoc.txt:12818: (SEVERE/4) Unexpected section title.
    +
    +  Sharing requirements and configs of source repository with shares
    +  -----------------------------------------------------------------
    +  Exiting due to level-4 (SEVERE) system message.
    +  [1]
```

This patch fixes that.

Differential Revision: https://phab.mercurial-scm.org/D9552

hgext/share.py

@@ -47,8 +47,7 b' The following ``share.`` config options '
 
 .. container:: verbose
 
-    Sharing requirements and configs of source repository with shares
-    -----------------------------------------------------------------
+    Sharing requirements and configs of source repository with shares:
 
     By default creating a shared repository only enables sharing a common
     history and does not share requirements and configs between them. This