Remove ink_primitives::hash module (#450)

* [primitives, lang/macro] remove ink_primitives::hash module

# Conflicts:
#	primitives/src/lib.rs

* [core] remove ink_core's Selector::{from_str, from<&[u8]>} constructors

* [examples] fix DNS contract

* [examples] fix ers20

* [examples] fix other example smart contracts

* [examples] apply rustfmt
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