Wallet: Remove all possible Mock data and feature flag code that is interacting with mock data.

[J-Son89]

To speed up the development of the wallet UI mock data was initially used. Now that there is enough development in place and the pattern for integration with the rpc is stabilised we should remove all mock data.

Buy Tokens List (options menu for "Buy" on account page) - should use rpc request - GetCryptoOnRamps available in the wallet.

Some other pieces using mock data:
Bridge Page
Wallet Account -> "Bridge" Button
Use real data for tokens

Collectibles Activity,
Generate New Keypair (in the create account flow),
Address suggestions etc
should all be hidden behind a feature flag of some sort so that an end user would not see this data.
Bridging a token

Example of how to feature flag:
#18530