Set save_mat=False

[chahank]

Changes proposed in this PR:

• This sets the variable ImpactCalc.impact(save_mat=False) to False in the unsequa module only. Since the change to the ImpactCalc class, the default was changed from False to True, thus it needs to be set explicitly now. This is important as it cost memory and computation time, while the information cannot be processed in the unsequa module at the moment.

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[chahank]

If you accept the fix, I will update the changelog.

[peanutfun]

@chahank Can you clarify in the PR description that this only affects the Unsequa module? Also, a Changelog entry is missing 🙃 Apart from that, everything looks good! 👌