Attempt to avoid specifying `BlockHashCount` for different...

Attempt to avoid specifying `BlockHashCount` for different `mocking::{MockBlock, MockBlockU32, MockBlockU128}` (#4543)

While doing some migration/rebase I came in to the situation, where I
needed to change `mocking::MockBlock` to `mocking::MockBlockU32`:
```
#[derive_impl(frame_system::config_preludes::TestDefaultConfig)]
impl frame_system::Config for TestRuntime {
	type Block = frame_system::mocking::MockBlockU32<TestRuntime>;
	type AccountData = pallet_balances::AccountData<ThisChainBalance>;
}
```
But actual `TestDefaultConfig` for `frame_system` is using `ConstU64`
for `type BlockHashCount = frame_support::traits::ConstU64<10>;`
[here](https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/system/src/lib.rs#L303).
Because of this, it force me to specify and add override for `type
BlockHashCount = ConstU32<10>`.

This PR tries to fix this with `TestBlockHashCount` implementation for
`TestDefaultConfig` which supports `u32`, `u64` and `u128` as a
`BlockNumber`.

### How to simulate error
Just by removing `type BlockHashCount = ConstU32<250>;`
[here](https://github.com/paritytech/polkadot-sdk/blob/master/substrate/frame/multisig/src/tests.rs#L44)
```
:~/parity/olkadot-sdk$ cargo test -p pallet-multisig
   Compiling pallet-multisig v28.0.0 (/home/bparity/parity/aaa/polkadot-sdk/substrate/frame/multisig)
error[E0277]: the trait bound `ConstU64<10>: frame_support::traits::Get<u32>` is not satisfied
   --> substrate/frame/multisig/src/tests.rs:41:1
    |
41  | #[derive_impl(frame_system::config_preludes::TestDefaultConfig)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `frame_support::traits::Get<u32>` is not implemented for `ConstU64<10>`
    |
    = help: the following other types implement trait `frame_support::traits::Get<T>`:
              <ConstU64<T> as frame_support::traits::Get<u64>>
              <ConstU64<T> as frame_support::traits::Get<std::option::Option<u64>>>
note: required by a bound in `frame_system::Config::BlockHashCount`
   --> /home/bparity/parity/aaa/polkadot-sdk/substrate/frame/system/src/lib.rs:535:24
    |
535 |         type BlockHashCount: Get<BlockNumberFor<Self>>;
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Config::BlockHashCount`
    = note: this error originates in the attribute macro `derive_impl` which comes from the expansion of the macro `frame_support::macro_magic::forward_tokens_verbatim` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0277`.
error: could not compile `pallet-multisig` (lib test) due to 1 previous error 
```




## For reviewers:

(If there is a better solution, please let me know!)

The first commit contains actual attempt to fix the problem:
https://github.com/paritytech/polkadot-sdk/commit/3c5499e5

.
The second commit is just removal of `BlockHashCount` from all other
places where not needed by default.

Closes: https://github.com/paritytech/polkadot-sdk/issues/1657

---------

Co-authored-by: Bastian Köcher <[email protected]>