[FEATURE] Install tool: Remove obsolete keys from LocalConfiguration

Some configuration settings are obsolete, but they have never been
actively removed from LocalConfiguration. The patch introduces a
list of obsolete configuration options (like SYS/extCache) to the
install tool step controller and silently removes those settings
from LocalConfiguration to keep it clean. This also obsoletes
some deprecation code within core bootstrap.

Change-Id: Id422801f5bbedc0f444a0d905bdbb7d736fd82e8
Resolves: #49299
Related: #49162
Releases: 6.2
Reviewed-on: https://review.typo3.org/21553
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn