operations/clean: make sure paccache keeps 3 pkgs

looks like .pacnew files don't generate properly unless theres like 3
packages in the pacman cache. why is pacman so confusing i swear nobody
knows how it works. well anyways this commit also removes the config
keys `paccache_keep` and `paccache_keep_ins_pkgs` as they shouldnt be
able to be changed.

src/internal/config.rs

@@ -17,8 +17,6 @@ pub struct Config {
 #[derive(Debug, Deserialize, Serialize)]
 pub struct ConfigBase {
     pub pacdiff_warn: bool,
-    pub paccache_keep: i32,
-    pub paccache_keep_ins_pkgs: bool,
     pub aur_verification_prompt: bool,
 }
 
@@ -37,8 +35,6 @@ impl Default for ConfigBase {
     fn default() -> Self {
         Self {
             pacdiff_warn: true,
-            paccache_keep: 0,
-            paccache_keep_ins_pkgs: true,
             aur_verification_prompt: true,
         }
     }

src/operations/clean.rs

@@ -83,14 +83,12 @@ pub async fn clean(options: Options) {
     let clear_pacman_cache = noconfirm || prompt!(default no, "Also clear pacman's package cache?");
 
     if clear_pacman_cache {
-        let conf = Config::read();
-
         // Clear pacman's cache
-        // keeps 0 versions of the package in the cache by default
-        // keeps installed packages in the cache by default
+        // keeps 3 versions of the package in the cache
+        // keeps installed packages in the cache
         let result = PaccacheBuilder::default()
-            .set_keep(conf.base.paccache_keep)
-            .keep_ins_pkgs(conf.base.paccache_keep_ins_pkgs)
+            .set_keep(3)
+            .keep_ins_pkgs(true)
             .quiet_output(quiet)
             .remove()
             .await;