[TASK] Remove unneded text in Install-Tool

Some text in the install tool should be removed

- "Installing TYPO3 as always been a hot topic on the mailinglist"...
  Nowadays it is quite easy to install TYPO3
- The text why the InstallTool should be standalone and no BE module is
  not quite true as it is also a BE module and rest of the text is such
  technical and got no information benefit for anybody

Change-Id: I73c312e6a426ef9fd3754564fa8fce707116a242
Resolves: #46547
Releases: 6.1
Reviewed-on: https://review.typo3.org/19176
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer