Revert "Reject weak hash algorithms as SRIs, and warn in any other cases"

This reverts commit 02c35ea9df.

Reason for revert: this code path is also used for `Input::getRev()`, i.e. flakes VCS revision validation, which, in the case of Git, are using SHA1.
As a result, this cause too much noise due to SHA1 revisions in Flakes.

Change-Id: I8064c1ebc26e4e83b627f0803a7a9ba56cfe1f37

src/libutil/hash.cc

@@ -8,7 +8,6 @@
 #include "hash.hh"
 #include "archive.hh"
 #include "charptr-cast.hh"
-#include "fmt.hh"
 #include "logging.hh"
 #include "split.hh"
 #include "strings.hh"
@@ -211,17 +210,6 @@ Hash Hash::parseNonSRIUnprefixed(std::string_view s, HashType type)
 Hash::Hash(std::string_view rest, HashType type, bool isSRI)
     : Hash(type)
 {
-    if (type == HashType::MD5 || type == HashType::SHA1) {
-        if (isSRI) {
-            // Forbidden as per https://w3c.github.io/webappsec-csp/#grammardef-hash-algorithm
-            throw BadHash("%s values are not allowed in SRI hashes", printHashType(type));
-        } else {
-            logWarning({
-                    .msg = HintFmt("%s hashes are considered weak, use a newer hashing algorithm instead. (value: %s)", Uncolored(printHashType(type)), rest)
-            });
-        }
-    }
-
     if (!isSRI && rest.size() == base16Len()) {
 
         auto parseHexDigit = [&](char c) {