For installed specifications, we can ignore any constraints they may
have, since we know they match the current version of Ruby or otherwise
would not be installed.

For remote specifications, we already resolve optimistically without
metadata and retry force-fetching it if necessary.

If in the future we support resolving against a Ruby version different
that the one being run, we'll probably need to change this but now it's
unnecessary and saves some memory.

### Before

Total allocated: 262.99 MB (3177437 objects)
Total retained:  115.91 MB (1297821 objects)

### After

Total allocated: 259.89 MB (3134199 objects)
Total retained:  115.05 MB (1283779 objects)

https://github.com/rubygems/rubygems/commit/201c1863fc