dnsdist: Remove autotool remants from Docker image build

[pieterlexis]

Short description

The image builds broke after #17010 was merged.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[romeroalx]

LGTM, thanks!

Test: https://github.com/PowerDNS/pdns/actions/runs/26745550191

[coveralls]

Coverage Report for CI Build 26745266863

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage decreased (-0.02%) to 72.066%

Details

• Coverage decreased (-0.02%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 3741 coverage regressions across 94 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

3741 previously-covered lines in 94 files lost coverage.

Top 10 Files by Coverage Loss	Lines Losing Coverage	Coverage
pdns/recursordist/syncres.cc	419	76.06%
pdns/recursordist/rec-lua-conf.cc	347	19.57%
pdns/recursordist/rec-rust-lib/cxxsupport.cc	341	57.92%
pdns/recursordist/rpzloader.cc	291	43.45%
pdns/recursordist/rec-main.hh	146	8.99%
pdns/ixfr.cc	118	40.06%
pdns/axfr-retriever.cc	105	13.65%
pdns/recursordist/recpacketcache.cc	96	55.33%
pdns/recursordist/rec-protozero.hh	83	17.8%
pdns/arguments.cc	76	37.25%

---

Coverage Stats

Relevant Lines:	132912
Covered Lines:	105523
Line Coverage:	79.39%
Relevant Branches:	64206
Covered Branches:	36532
Branch Coverage:	56.9%
Branches in Coverage %:	Yes
Coverage Strength:	4256665.78 hits per line

---

💛 - Coveralls

[rgacogne]

I'm going to merge this, the auth failure was fixed in #17491