Revert "[SIC] Make non-const the QRegExp methods that modify the internals"

Revert "[SIC] Make non-const the QRegExp methods that modify the internals"

This reverts commit 75a0c7f9b52cde47f20fdc1b89e1264d60350848. The
source-incompatible change proved to be more trouble than it's
worth. Too much intrusion into the porting effort of applications for
no appreciable gain, especially considering that we have a replacement
class.

Change-Id: Ia99a2360390a2062a8ddb6e12c8f2099287a2704
Discussed-on: http://lists.qt-project.org/pipermail/development/2012-May/003562.html
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>