Don't pin buildToolsVersion

fdroidserver forces its own build-tools version into app builds, but that
rewrite only matches files ending .gradle — not .gradle.kts. So the pin
would have survived onto their buildserver, and if it could not get
build-tools 36.0.0 the build would fail rather than fall back. AGP picks
its own default instead. Clean rebuild is unaffected: still builds, still
zero permissions.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -7,7 +7,6 @@ plugins {
 android {
     namespace = "nl.hansdezwart.bgclock"
     compileSdk = 36
-    buildToolsVersion = "36.0.0"
 
     defaultConfig {
         applicationId = "nl.hansdezwart.bgclock"