Implement tests for DEX Module LP command: removeLiquidity

[emiliolisk]

Description

removeLiquidity was tested with the following scenarios and expectations as mentioned below:

Scenario	Expectation
Should be successful when all the parameters are correct	Calls token methods and emits removeLiquidity event.
Should not be successful when current timestamp is over maxTimestampValid	Exception is thrown.
Should terminate and throw error if positionsStore doesn't have position with the specified positionID	Exception is thrown.
Should terminate due to liquidityToRemove > totalLiquidity	Exception is thrown.
Should terminate and throw error as amount1Min > amount1	Exception is thrown.
Should terminate and throw error as amount0Min > amount0	Exception is thrown.

Acceptance Criteria

• Existing and new unit tests are passing

[Naureen1lightcurve]

This issue #277 is already resolved and the last modification is in this commit.