Since the \br was promoted from a macro to a QDoc command, its output
has been enclosed in extra paragraph end/start tags, adding to the
visible vertical space.

This change fixes the issue by not closing the paragraph when QDoc
encounters a \br command.

Also removes the now-obsolete \br and \hr macros, as they are both
proper commands. \BR and \HR substitute macros are kept.

Task-number: QTBUG-37361
Change-Id: Iabbefb6e79268419792ccba42386f6342ccd175d
Reviewed-by: Martin Smith <martin.smith@digia.com>