Rspamd: minor tweaks and follow-up for SPF, DKIM and DMARC symbols

[georglauterbach]

Follow-up of #3913, providing only

1. renaming of a file;
2. two composite symbol re-definitions.

Review commit by commit.

composites.conf is important because the default policy of these composite symbols I re-defined is remove_weight, which is precisely what we do not want to happen. I noticed this issue only when looking at my Rspamd history recently; I also had to open a bug report over at rspamd/rspamd to find the root cause.

Type of change

• Improvement (non-breaking change that does improve existing functionality)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary, I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have added information about changes made in this PR to CHANGELOG.md