Revert "H2O: Use 2 database connections per thread again (#9176)" (#9223)

This reverts commit 57f2f117488029a625feea0605f7da76bfb2a0b9.

frameworks/C/h2o/h2o.dockerfile

@@ -109,4 +109,4 @@ CMD ["taskset", \
      "dbname=hello_world host=tfb-database password=benchmarkdbpass sslmode=disable user=benchmarkdbuser", \
      "-f", \
      "/opt/h2o_app/share/h2o_app/template", \
-     "-m2"]
+     "-m1"]