Stop using CallData in Multisig doc test

[HCastano]

The example we were providing in the add_owner documentation of the Multisig example
used CallData, which is only available in the off-chain testing engine. This meant that
if contract authors used this example vertabim in their contracts (which is totally
reasonable in this case) their contracts wouldn't compile.

I've changed the example to use things that would be available to contract authors so
in order to make the example more copy-pastable.

Closes #1197 again 😅

[codecov-commenter]

Codecov Report

Merging #1202 (498eaee) into master (2437357) will increase coverage by 17.59%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #1202       +/-   ##
===========================================
+ Coverage   61.71%   79.30%   +17.59%     
===========================================
  Files         228      228               
  Lines        8637     8637               
===========================================
+ Hits         5330     6850     +1520     
+ Misses       3307     1787     -1520     

Impacted Files	Coverage Δ
crates/storage/src/traits/impls/prims.rs	96.92% <0.00%> (+1.53%)	⬆️
crates/lang/ir/src/ir/attrs.rs	82.27% <0.00%> (+3.87%)	⬆️
...ates/storage/src/collections/hashmap/fuzz_tests.rs	100.00% <0.00%> (+4.25%)	⬆️
crates/metadata/src/layout/mod.rs	77.01% <0.00%> (+4.59%)	⬆️
crates/lang/ir/src/ir/trait_def/item/mod.rs	90.16% <0.00%> (+4.91%)	⬆️
crates/env/src/engine/off_chain/test_api.rs	90.00% <0.00%> (+6.00%)	⬆️
crates/lang/ir/src/ir/item_impl/constructor.rs	93.84% <0.00%> (+6.15%)	⬆️
crates/env/src/engine/off_chain/impls.rs	43.03% <0.00%> (+8.22%)	⬆️
crates/lang/ir/src/ir/idents_lint.rs	71.42% <0.00%> (+9.52%)	⬆️
crates/env/src/api.rs	33.33% <0.00%> (+9.52%)	⬆️
... and 50 more

---

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[paritytech-cicd-pr]

🦑 📈 ink! Example Contracts ‒ Changes Report 📉 🦑

These are the results when building the examples/* contracts from this branch with cargo-contract 1.1.0-2b7b50f and comparing them to ink! master:

	Δ Optimized Size	Δ Used Gas	Total Optimized Size	Total Used Gas
accumulator			1.03 K
adder			2.17 K
contract-introspection			2.37 K
contract-terminate			0.94 K	214_418
contract-transfer			8.15 K	14_418
delegate-calls			2.99 K	14_950
delegator			6.37 K	46_295
dns			8.84 K	43_254
erc1155			17.23 K	86_508
erc20			8.49 K	43_254
erc721			11.81 K	115_344
flipper			1.31 K	14_418
forward-calls			2.90 K	29_536
incrementer			1.21 K	14_418
multisig			25.20 K	93_527
rand-extension			3.92 K	14_418
subber			2.19 K
trait-erc20			8.76 K	43_254
trait-flipper			1.00 K	14_418
trait-incrementer			1.19 K	28_836
upgradeable-flipper			1.55 K

Link to the run | Last update: Sun Mar 27 05:46:30 CEST 2022