crypto-common: remove std feature

As of #1660, the `crypto-common` crate stopped linking `std` entirely by
switching to `core::error::Error`.

That PR didn't remove the `std` feature however, which was retained to
transitively activate the `std` features of `getrandom` and `rand_core`
optioinally in the event their corresponding features are enabled.

This PR goes ahead and removes it entirely, which also unblocks being
able to remove the `std` feature from other crates like `aead`,
`cipher`, `digest`, and `universal-hash`.

Author: tarcieri

aead/Cargo.toml

@@ -27,7 +27,7 @@ heapless = { version = "0.8", optional = true, default-features = false }
 [features]
 default = ["rand_core"]
 alloc = []
-std = ["alloc", "crypto-common/std"]
+std = ["alloc"]
 dev = ["blobby"]
 getrandom = ["crypto-common/getrandom"]
 rand_core = ["crypto-common/rand_core"]

cipher/Cargo.toml

@@ -22,7 +22,7 @@ zeroize = { version = "1.8", optional = true, default-features = false }
 
 [features]
 alloc = []
-std = ["alloc", "crypto-common/std"]
+std = ["alloc"]
 block-padding = ["inout/block-padding"]
 # Enable random key and IV generation methods
 rand_core = ["crypto-common/rand_core"]

crypto-common/Cargo.toml

@@ -21,7 +21,6 @@ getrandom = { version = "0.2", optional = true }
 
 [features]
 getrandom = ["dep:getrandom", "rand_core?/getrandom"]
-std = ["getrandom?/std", "rand_core?/std"]
 
 [package.metadata.docs.rs]
 all-features = true

digest/Cargo.toml

@@ -30,7 +30,7 @@ rand_core = ["crypto-common/rand_core"] # Enable random key generation methods
 oid = ["const-oid"]
 zeroize = ["dep:zeroize", "block-buffer?/zeroize"]
 alloc = []
-std = ["alloc", "crypto-common/std"]
+std = ["alloc"]
 dev = ["blobby"]
 
 [package.metadata.docs.rs]

universal-hash/Cargo.toml

@@ -17,7 +17,7 @@ crypto-common = "0.2.0-rc.0"
 subtle = { version = "2.4", default-features = false }
 
 [features]
-std = ["crypto-common/std"]
+std = []
 
 [package.metadata.docs.rs]
 all-features = true