[TASK] Make use of .t3-table in EXT: extension manager

Use <table class="t3-table"> in backend module.

Removes duplicate SASS/CSS definitions in module in order
to make use of central core styles.

Change-Id: I174d63ab9014ec35842a7bd55863ed0113a669fe
Resolves: #55127
Releases: 6.2
Reviewed-on: https://review.typo3.org/26923
Reviewed-by: Marcin Sągol
Tested-by: Marcin Sągol
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters