fdo#75757: remove inheritance to std::vector

... which was introduced at 2110397670695991b3a5cd28a15ba0ffd2a3a611.

Change-Id: If0f634b29e1891574267edf8cc07b24d07a9406c
Reviewed-on: https://gerrit.libreoffice.org/10363
Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>