fix Managed pools tokens weights

[mendesfabio]

The weight attribute is null for Managed pools tokens. After a quick investigation, I found that:

• weights are never set at the creation because Managed has pre-minted BPT - this condition is always falsy
• updatePoolWeights is not called on every Managed pool Swap event

Requirements

• Add Managed to isVariableWeightPool function
• Remove BPT from tokensList before comparing to weights

[mendesfabio]

I deployed a fix to staging -- will get back into this after sync is complete (hopefully Monday)