fix: enable -Wcast-qual flag for libcrypto=awslc

[boquan-fang]

Resolved issues:

Resolve issue #4710

Description of changes:

• Remove the condition which only add -Wcast-qual back for non AWS-lc Libcrypto.

Call-outs:

• Waiting for awslc update for ubuntu18.

Testing:

• Local testing without specifying S2N_LIBCRYPTO=openssl.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.