Remove deprecated expandvar converter #24678

Job	Run time
setup-environment	52s
govulncheck	1m 32s
test-coverage	8m 56s
unittest-matrix (ubuntu-latest, ~1.23)	5m 17s
checks	2m 13s
unittest-matrix (ubuntu-latest, ~1.22)	5m 11s
cross-build-collector (darwin, amd64)	48s
lint	4m 34s
cross-build-collector (darwin, arm64)	48s
cross-build-collector (linux, 386)	46s
cross-build-collector (linux, amd64)	1m 14s
cross-build-collector (linux, arm64)	57s
cross-build-collector (linux, ppc64le)	54s
cross-build-collector (linux, arm, 7)	46s
cross-build-collector (linux, s390x)	45s
cross-build-collector (windows, 386)	45s
cross-build-collector (windows, amd64)	54s
unittest	1s
	37m 13s

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