Get rid of the libc crate dependency in bssl-sys

It appears to no longer be needed.

Change-Id: Idd9aa128192eb0f1bdff52e190fd032090411d43
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/58165
Auto-Submit: Bob Beck <bbe@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Reviewed-by: Nabil Wadih <nwadih@google.com>

rust/bssl-crypto/deny.toml

@@ -168,9 +168,6 @@ allow = [
     { name = "bssl-crypto", version = "=0.1.0" },
     # bssl-sys should be allowed, version appropriately.
     { name = "bssl-sys", version = "=0.1.0" },
-    # libc is used by bssl-sys from android, but is not really needed and should
-    # be removed once this can be checked with android.
-    { name = "libc", version = "=0.2.140" },
     # hex-literal was added for ease of tests, but should be removed.
     { name = "hex-literal", version = "=0.3.4" },
 ]

rust/bssl-sys/Cargo.toml

@@ -7,4 +7,3 @@ publish = false
 license = "MIT"
 
 [dependencies]
-libc = "0.2"