[CLEANUP] Cleanup EXT:rsaauth

EXT:rsaauth has several minor flaws codewise that make
PHPStorms inspection go wild:
* Clean up direct usage of $GLOBALS[TYPO3_DB].
* TCA of tx_rsaauth_keys is not needed and can be removed, as a
result, "Oops! You should not see this" no longer shows
up in db_lowlevel.

Resolves: #62623
Releases: master
Change-Id: I865a9bd3f3f0ff681ba0838a8cbb3a14b885e44f
Reviewed-on: http://review.typo3.org/33712
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@wmdb.de>
Tested-by: Mathias Schreiber <mathias.schreiber@wmdb.de>