build: remove unused regex dependency

Author: ldm0

rrule/Cargo.toml

@@ -16,7 +16,6 @@ edition.workspace = true
 chrono = "0.4.39"
 chrono-tz = "0.10.1"
 log = "0.4.25"
-regex = { version = "1.11.1", default-features = false, features = ["perf", "std"] }
 clap = { version = "4.5.26", optional = true, features = ["derive"] }
 thiserror = "2.0.11"
 serde_with = { version = "3.12.0", optional = true }