gimptextlayout-render.c: Don't apply matrix transformtion
Text layout matrix transformation is just the identity transformation for now (in the future more transformations will be added to support non-destructively transforming a text layer), when the xres != yres, some floating point rounding errors might occur, causing the text to be shifted to the right/left.
For now, we can safely disable the matrix transformation, however a better solution is needed for when other transformations will be added.
Closes #1028