chore!: remove alias exports `DefaultContext` and `EyreContext` #473

Job	Run time
Clippy (stable)	26s
Rustfmt (stable)	4s
Miri	1m 21s
Check (stable)	29s
Test Suite (stable)	1m 1s
Test Suite	2m 55s
Test Suite (ubuntu-latest)	1m 2s
Test Suite (stable, --no-default-features)	56s
Test Suite (--no-default-features)	2m 48s
Test Suite (windows-latest)	1m 48s
Test Suite (stable, --no-default-features --features track-caller)	57s
Test Suite (--no-default-features --features track-caller)	2m 55s
Test Suite (macOS-latest)	1m 44s
Test Suite (stable, --no-default-features --features auto-install)	56s
Test Suite (--no-default-features --features auto-install)	2m 49s
Test Suite (stable, --features pyo3)	1m 1s
Test Suite (stable, --all-features)	1m 45s
Test Suite (beta)	1m 9s
Test Suite (beta, --no-default-features)	1m 4s
Test Suite (beta, --no-default-features --features track-caller)	1m 0s
Test Suite (beta, --no-default-features --features auto-install)	1m 12s
Test Suite (beta, --features pyo3)	1m 6s
Test Suite (beta, --all-features)	1m 14s
Test Suite (nightly)	1m 8s
Test Suite (nightly, --no-default-features)	1m 10s
Test Suite (nightly, --no-default-features --features track-caller)	1m 6s
Test Suite (nightly, --no-default-features --features auto-install)	1m 6s
Test Suite (nightly, --features pyo3)	1m 9s
Test Suite (nightly, --all-features)	1m 8s
	38m 29s

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