Doc: Remove space between class name and method name

Previously, the generated documentation contained
"QFutureWatcher:: progressValueChanged()". While it is legal C++, it
prevented QDoc from auto-linking to the QFutureWatcher class reference.

Change-Id: I2cace763f1825b0b4478b2bde95679d25df8bb5e
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Doc: Remove duplicated Qt Concurrent overview

- The "Concurrent Programming" page is an exact duplicate of the Qt Concurrent module landing
  page.
- The "qtconcurrent intro" target is not referenced anywhere.

Change-Id: Ice9b4360783013fe972258ca54a0004be43b8766
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>