internal/global imports testing

[aaronbee]

Description

go.opentelemetry.io/otel has a dependency on the standard library "testing" package. Any production binary that depends on otel will end up including the "testing" library, which is unnecessary bloat. This import was added in #2754 in internal/global/state.go.

Environment

• OS: N/A
• Architecture: N/A
• Go Version: go1.17
• opentelemetry-go version: v1.6.3

Steps To Reproduce

go list -deps go.opentelemetry.io/otel | grep '^testing$'

Expected behavior

Production packages should not import "testing".