lua: remove digest.sha() and digest.sha_hex()

SHA-0 is considered weak for years and was removed in OpenSSL since
1.1.0.

These Lua functions did not work since 15ed10e4, but give 'Digest
method "sha" is not supported' error for any input. Removed them to
don't confuse a user with a Tab completion.

Follow up #1722.
Fixes #4028.

src/lua/crypto.lua

@@ -58,7 +58,7 @@ end
 local digests = {}
 for class, name in pairs({
     md2 = 'MD2', md4 = 'MD4', md5 = 'MD5',
-    sha = 'SHA', sha1 = 'SHA1', sha224 = 'SHA224',
+    sha1 = 'SHA1', sha224 = 'SHA224',
     sha256 = 'SHA256', sha384 = 'SHA384', sha512 = 'SHA512',
     dss = 'DSS', dss1 = 'DSS1', mdc2 = 'MDC2', ripemd160 = 'RIPEMD160'}) do
     local digest = ffi.C.EVP_get_digestbyname(class)

src/lua/digest.lua

@@ -36,7 +36,6 @@ local BASE64_NOWRAP = 2
 local BASE64_URLSAFE = 7
 
 local digest_shortcuts = {
-    sha     = 'SHA',
     sha224  = 'SHA224',
     sha256  = 'SHA256',
     sha384  = 'SHA384',