Standardize usage of Snakemake's "config" variable

Checking presence of a key in the config should be done with the
membership operator.

Snakefile

@@ -25,7 +25,7 @@ include: "workflow/snakemake_rules/glycosylation.smk"
 include: "workflow/snakemake_rules/clades.smk"
 
 
-if config.get("deploy_url"):
+if "deploy_url" in config:
     include: "workflow/snakemake_rules/nextstrain_automation.smk"
 
 rule clean:

ingest/Snakefile

@@ -25,7 +25,7 @@ def _get_all_targets(wildcards):
             )
         elif len(remote_file_names) != len(set(remote_file_names)):
             print(f"Skipping file upload for {target!r} because there are duplicate remote file names.")
-        elif not config.get("s3_dst"):
+        elif "s3_dst" not in config:
             print(f"Skipping file upload for {target!r} because the destintion was not defined.")
         else:
             all_targets.extend(