Remove attribute data-htmlarea-file-table from RTE

Images in RTE are now Processed Files. As a result
it makes little sense to store the table name of a File
since "sys_file" is the unique possible value.
The change-set removes attribute "data-htmlarea-file-table"
from the RTE, e.g.:

data-htmlarea-file-table="sys_file"

Change-Id: If8bde0822629cab2acb8b9dbdf9337f599da64b9
Releases: master
Resolves: #56996
Reviewed-on: http://review.typo3.org/28470
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>