Revert "run: add shaderdb flag for v3d"

This reverts commit 47ded5b3.

Mistake on my part, `V3D_DEBUG=shaderdb` is actually for manually
dumping stats from random apps in the shader-db format so that they can
be read using shader-db's `report.py`.

Having `V3D_DEBUG=shaderdb` in shader-db makes it dump the information
twice, causing issues.

Signed-off-by: Eric Engestrom <eric@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>