[pool] Issue with gas efficiency check for v0.6 using a paymaster

[dancoombs]

Describe the bug
The check incorporates a post op estimated cost of 2*VGL, even if a post op isn't used, if VGL >> CGL, and a post op isn't used at all, then gas eff will be low.

To reproduce
Send a UO with the properties above and a gas limit eff of 15%, typically triggers and rejects the UO.

Expected behavior
This shouldn't reject the UO, for v0.6 we shouldn't include the post op gas at all in this calculation.