chore: remove unused method from Bitfield class (#41)

`Bitfield.prototype.clear` was never used, so we can remove it.

lib/bitfield.js

@@ -106,17 +106,6 @@ class Bitfield {
     this.unflushed?.push(p)
   }
 
-  /** @returns {Promise<void>} */
-  clear() {
-    return new Promise((resolve, reject) => {
-      if (!this.storage) return resolve()
-      this.storage.del(0, Infinity, (err) => {
-        if (err) reject(err)
-        else resolve()
-      })
-    })
-  }
-
   /** @returns {Promise<void>} */
   close() {
     return new Promise((resolve, reject) => {