Remove default to 18 decimals in quotesToRenderableData method

[danjm]

Fixes an issue where tokens with 0 decimals would show incorrect amounts on the view token screen.

The default to 18 decimals was unnecessary, as we validate /tokens api responses in swaps.util.js to verify that decimals are defined and either a number or a string of decimal digits between 0 and 36. If the decimals were somehow undefined by the time quotesToRenderableData in view-quote.js, then it would be better that a user hit an error than be shown an incorrect default.

A future improvement will be to add data validation to the quotesToRenderableData method

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[brad-decker]

LGTM

[metamaskbot]

Builds ready [87883ea]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• code coverage: Report
• dep viz: background
• all artifacts

Page Load Metrics (475 ± 48 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	31	64	43	10	5
		domContentLoaded	308	589	474	101	48
		load	309	590	475	100	48
		domInteractive	308	589	474	100	48