Remove custom extension readme/changelog URLs

These were barely used/maintained, so just killing them.
Changelog menu item still exists to take you to the relevant git history.

app/src/main/java/eu/kanade/tachiyomi/extension/model/Extension.kt

@@ -13,8 +13,6 @@ sealed class Extension {
     abstract val libVersion: Double
     abstract val lang: String?
     abstract val isNsfw: Boolean
-    abstract val hasReadme: Boolean
-    abstract val hasChangelog: Boolean
 
     data class Installed(
         override val name: String,
@@ -24,8 +22,6 @@ sealed class Extension {
         override val libVersion: Double,
         override val lang: String,
         override val isNsfw: Boolean,
-        override val hasReadme: Boolean,
-        override val hasChangelog: Boolean,
         val pkgFactory: String?,
         val sources: List<Source>,
         val icon: Drawable?,
@@ -43,8 +39,6 @@ sealed class Extension {
         override val libVersion: Double,
         override val lang: String,
         override val isNsfw: Boolean,
-        override val hasReadme: Boolean,
-        override val hasChangelog: Boolean,
         val sources: List<Source>,
         val apkName: String,
         val iconUrl: String,
@@ -75,7 +69,5 @@ sealed class Extension {
         val signatureHash: String,
         override val lang: String? = null,
         override val isNsfw: Boolean = false,
-        override val hasReadme: Boolean = false,
-        override val hasChangelog: Boolean = false,
     ) : Extension()
 }