VP8LDoFillBitWindow: remove stale TODO
VP8LDoFillBitWindow: remove stale TODO

the read size may be fixed, but the offsets into buf_ are not. forcing
an aligned read then shifting or using a temporary would be costly. this
is less important now that WebPMemToUint32() is being used.

Change-Id: I357fec8f750969cce91987abebed2f95e27a835f

webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp