chore!: remove alias exports `DefaultContext` and `EyreContext` #468

Job	Run time
Test Suite (ubuntu-latest)	1m 11s
Test Suite	2m 51s
Test Suite (windows-latest)	1m 46s
Test Suite (--no-default-features)	2m 38s
Check (stable)	14s
Test Suite (macOS-latest)	52s
Rustfmt (stable)	6s
Test Suite (--no-default-features --features track-caller)	2m 38s
Test Suite (--no-default-features --features auto-install)	2m 40s
Test Suite (stable)	1m 2s
Clippy (stable)	22s
Miri	1m 19s
Test Suite (stable, --no-default-features)	52s
Test Suite (stable, --no-default-features --features track-caller)	52s
Test Suite (stable, --no-default-features --features auto-install)	59s
Test Suite (stable, --features pyo3)	1m 3s
Test Suite (stable, --all-features)	1m 10s
Test Suite (beta)	1m 7s
Test Suite (beta, --no-default-features)	58s
Test Suite (beta, --no-default-features --features track-caller)	1m 3s
Test Suite (beta, --no-default-features --features auto-install)	1m 2s
Test Suite (beta, --features pyo3)	1m 7s
Test Suite (beta, --all-features)	1m 14s
Test Suite (nightly)	1m 8s
Test Suite (nightly, --no-default-features)	1m 6s
Test Suite (nightly, --no-default-features --features track-caller)	1m 4s
Test Suite (nightly, --no-default-features --features auto-install)	1m 4s
Test Suite (nightly, --features pyo3)	1m 11s
Test Suite (nightly, --all-features)	1m 9s
	35m 48s

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