Revert "GeometryShaderGen: Don't use centroid in for input variables."

[degasus]

This reverts commit 4cbaddb.

Specs say this centroid is allowed, and this commit breaks geometry shader support on all drivers.

[Sonicadvance1]

LGTM

[dolphin-emu-bot]

FifoCI detected that this change impacts graphical rendering. Here are the behavior differences detected by the system:

• chibi-robo-fastdepth on ogl-lin-mesa: diff
• chibi-robo-zfighting on ogl-lin-mesa: diff
• line-width-test on ogl-lin-mesa: diff
• megaman-heat on ogl-lin-mesa: diff
• monkeyball-fuse on ogl-lin-mesa: diff
• rs2-zfreeze on ogl-lin-mesa: diff
• sf-assault-flashing on ogl-lin-mesa: diff
• ssbm-pointsize on ogl-lin-mesa: diff
• thps4-shadow on ogl-lin-mesa: diff
• ztp-grass on ogl-lin-mesa: diff
• chibi-robo-fastdepth on ogl-lin-nv: diff
• chibi-robo-zfighting on ogl-lin-nv: diff
• line-width-test on ogl-lin-nv: diff
• megaman-heat on ogl-lin-nv: diff
• monkeyball-fuse on ogl-lin-nv: diff
• rs2-zfreeze on ogl-lin-nv: diff
• sf-assault-flashing on ogl-lin-nv: diff
• ssbm-pointsize on ogl-lin-nv: diff
• thps4-shadow on ogl-lin-nv: diff
• ztp-grass on ogl-lin-nv: diff

_{^{automated-fifoci-reporter}}