You can remove (ie:clean, or reset to zero) a single bone's influence, you can use weight tools, like this:
edit: follow-up after a comment.
...imho it works 100%, but since moving that bone moves other connected bones (eg: thigh.L), which have weights are still infuencing the mesh... you see some influence, but from other bones.
This happen salso deactivating "deform" checkbox, as suggested by the other answer.
Deactivating "deform" checkbox keeps weight and thus, influence but it deactivates its evaluation (for that bone). Using clean you reset to zero the influence (useful maybe if you wish to start over painting it)