Update S3 features and make S3 support optional

Cargo.toml

@@ -19,7 +19,6 @@ rocket = "0.4.11"
 rocket_contrib = { version = "0.4.11", features = ["json"] }
 rocket_i18n = "0.4.1"
 scheduled-thread-pool = "0.2.6"
-#aws-creds = { version = "0.34", default-features = false, features = ["native-tls"] }
 serde = "1.0.137"
 serde_json = "1.0.81"
 shrinkwraprs = "0.3.0"
@@ -69,7 +68,7 @@ ructe = "0.15.0"
 rsass = "0.26"
 
 [features]
-default = ["postgres", "s3"]
+default = ["postgres"]
 postgres = ["plume-models/postgres", "diesel/postgres"]
 sqlite = ["plume-models/sqlite", "diesel/sqlite"]
 debug-mailer = []