cleanup hide testing PR (#11638)

# Description

This PR cleans up https://github.com/nushell/nushell/pull/11331. One
line was missed that caused the CI to break.

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crates/nu-std/std/mod.nu

@@ -9,7 +9,6 @@ export module input.nu
 export module iter.nu
 export module log.nu
 export module math.nu
-export module testing.nu
 export module xml.nu
 export-env {
     use dirs.nu []