Ensure permissions log only stores JSON-able data

[rekmarks]

This PR ensures that the permissions log will only store JSON-able data. I encountered this problem will building for snaps. This is unlikely, probably even impossible, to occur on develop at the moment, but the fix is cheap. It's accomplished as follows:

• Replace deep clone of JSON-RPC request and response objects in permissions log with stringification via fast-safe-stringify
• Add fast-safe-stringify as production dependency
  • It was already in our dependency graph, used by eth-rpc-errors and probably others

Additionally, makes the following related but distinct change:

• Remove safe-json-stringify from production dependencies
  • This dependency was unused. In the choice between it and fast-safe-stringify, the latter appears to be more widely used, and will remain our dependency graph regardless. Removing safe-json-stringify as a direct dependency removed it from our lockfile.

[metamaskbot]

Builds ready [bdc6d42]

• builds: chrome, firefox, opera
• bundle viz: background, ui, inpage, contentscript, ui-libs, bg-libs, phishing-detect
• build viz: Build System
• code coverage: Report
• storybook: Storybook
• all artifacts

Page Load Metrics (601 ± 21 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	47	70	58	7	3
		domContentLoaded	544	744	599	43	21
		load	545	746	601	43	21
		domInteractive	543	744	598	43	21