Merge #11173: RPC: Fix currency unit string in the help text

Merge #11173: RPC: Fix currency unit string in the help text

47ba2c312 Fix currency/fee-rate unit string in the help text (Akio Nakamura)

Pull request description:

  1. The RPC help text should use the constant `CURRENCY_UNIT` defined in `policy/feerate.cpp` instead of the literal `'BTC'`.
    In the following 2 RPC commands, `'BTC'` is written directly in the help text.
    This commit changes them to use that constant.
       1) `estimatesmartfee`
       2) `estimaterawfee`

  2. Some RPC command use `'satoshis'` as the unit.
    It should be written as `'satoshis'` instead of `'Satoshis'` in the RPC help text.
    So, this commit fixes this typo in `getblocktemplate`.

Tree-SHA512: d0bd1cd90560e59bf456b076b958a2a1c998f85a7e65aeb6b2abcaba18919a3ae62f7c3909210461084c1a3275a35b6ba3ea3ec8f5cce33702ffe383c9e84bce