[Widget] Remove back button when in token graph view

[srirambv]

Description

Two back buttons are shown when a token view is selected. Back button to token list can be missed as the back button to opt-in state is more obvious and can take back user to opt-in state instead of back to the token list

Steps to Reproduce

1. Open Crypto.com widget
2. Enable market view and select a token
3. Two back buttons are shown one on top which and next to token

Actual result:

Expected result:

Only have one back button on token graph view

Reproduces how often:

Easy

Brave version (brave://version info)

Brave	1.16.67 Chromium: 86.0.4240.111 (Official Build) (64 Bit)
Revision	b8c36128a06ebad76af51591bfec980224db5522-refs/branch-heads/4240@{#1290}
OS	All

Version/Channel Information:

• Can you reproduce this issue with the current release? NA
• Can you reproduce this issue with the beta 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:

[kjozwiak]

Adding release/blocking and moved into the 1.16.x milestone as we want this released with 1.16.x.

[GeetaSarvadnya]

Verification passed on

Brave | 1.16.68 Chromium: 86.0.4240.111 (Official Build) (64-bit)
-- | --
Revision | b8c36128a06ebad76af51591bfec980224db5522-refs/branch-heads/4240@{#1290}
OS | Windows 10 OS Version 1903 (Build 18362.1139)

• Reproduced the issue in 1.16.67
  
• Upgraded profile to 1.16.78 and ensured there is only one back arrow in the token graph view
  

[srirambv]

Verification passed on

Brave	1.16.68 Chromium: 86.0.4240.111 (Official Build) (x86_64)
Revision	b8c36128a06ebad76af51591bfec980224db5522-refs/branch-heads/4240@{#1290}
OS	macOS Version 10.15.7 (Build 19H2)

• Verified back button is only shown in token list view and is hidden when token details is opened
  

---

Verification passed on

Brave	1.16.68 Chromium: 86.0.4240.111 (Official Build) (64 bit)
Revision	b8c36128a06ebad76af51591bfec980224db5522-refs/branch-heads/4240@{#1290}
OS	Windows 10 OS Version 1809 (Build 17763.1518)

• Verified back button is only shown in token list view and is hidden when token details is opened
  

---

Verification passed on

Brave	1.16.68 Chromium: 86.0.4240.111 (Official Build) (64 bit)
Revision	b8c36128a06ebad76af51591bfec980224db5522-refs/branch-heads/4240@{#1290}
OS	Linux

• Verified back button is only shown in token list view and is hidden when token details is opened