Dont default gas limit in gas popover when non is available on transaction params

[danjm]

This PR removes the default value for gas limit in our gas editing popover. This case will only occur if no gas limit was suggested by a dapp, and calls to eth_estimateGas have failed not due to a simulation error, but a network failure. This would happen if the user is disconnected from the internet, or there is a failure connecting to the provider. In such a case, defaulting to 0 is safe because it requires the user to be intentional about the gas limit.

[github-actions]

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[metamaskbot]

Builds ready [a4a091d]

• builds: chrome, firefox, opera
• build viz: Build System
• code coverage: Report
• storybook: Storybook
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6, 7, 8
  • common: 0, 1, 2, 3
  • contentscript: contentscript
  • disable-console: disable-console
  • inpage: inpage
  • phishing-detect: 0
  • sentry-install: sentry-install
  • ui: 0, 1, 2, 3, 4, 5

Page Load Metrics (703 ± 38 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	56	88	69	9	4
		domContentLoaded	613	870	702	78	38
		load	614	871	703	78	38
		domInteractive	613	869	701	78	37

[tmashuang]

LGTM as it stands. There are cases where the gas limit will be provided by a dapp, and if the gas api/eth_gasPrice is sluggish or down altogether, there will not be an error on the confirm tx screen which users might question as to why they won't be able to confirm the proposed tx.