crypto/internal/fips140/drbg: unnecessary linear memory increase on Wasm with Go 1.26 [1.26 backport]

[gopherbot]

@cherrymui requested issue #78321 to be considered for backport to the next 1.26 minor release.

@gopherbot please backport this to Go 1.26. This is a change in 1.26 causing a significant memory usage increase. Thanks.

[gopherbot]

Change https://go.dev/cl/767320 mentions this issue: [release-branch.go1.26] crypto/internal/fips140/drbg: build tag out entropy generation on Wasm