[Desktop] Convert to asset doesn't auto update

[srirambv]

Description

Asset to be converted doesn't auto change

Steps to Reproduce

1. Connect to Binance widget
2. Set BTC to convert to BNB
3. Change BTC to DASH
4. BNB is retained even though DASH can only be converted to BUSD or USDT

Actual result:

Asset to be converted doesn't auto change

Expected result:

Convert to asset should auto updated based on selection of convert from asset

Reproduces how often:

Easy

Brave version (brave://version info)

Brave	1.8.85 Chromium: 81.0.4044.122 (Official Build) (64-bit)
Revision	44f4233f08910d83b146130c1938256a2e05b136-refs/branch-heads/4044@{#963}
OS	All

Version/Channel Information:

• Can you reproduce this issue with the current release? Yes
• Can you reproduce this issue with the beta channel? Yes
• Can you reproduce this issue with the dev channel? Yes
• Can you reproduce this issue with the nightly channel? Yes

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? NA
• Does the issue resolve itself when disabling Brave Rewards? NA
• Is the issue reproducible on the latest version of Chrome? NA

Miscellaneous Information: