Clear AccountTracker accounts and CachedBalances on createNewVaultAndRestore

[tmashuang]

Resets accounts in AccountTracker and CachedBalances when importing a new seed phrase, createNewVaultAndRestore is called.

[metamaskbot]

Builds ready [b282364]

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

Page Load Metrics (665 ± 31 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	28	80	41	14	7
		domContentLoaded	582	790	664	65	31
		load	583	791	665	65	31
		domInteractive	581	789	663	65	31

[Gudahtt]

LGTM!

I don't think this fixes the error shown, but clearing accounts and balances upon import does seem like a generally safe thing to do. There's probably some error this prevents.

[metamaskbot]

Builds ready [42c84ac]

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

Page Load Metrics (631 ± 30 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	30	84	43	17	8
		domContentLoaded	404	738	629	62	30
		load	406	740	631	62	30
		domInteractive	404	738	629	62	30