vt(4): Remove vt_buf->vb_dirtymask

This structure and the associated functions were unused since the
implementation of vd_bitblt_text_t callbacks.

MFC after:	3 days


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271868 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Fix inverted expression to report block size in mode page block descriptor.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@271869 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f