fix: remove build timestamp (breaking reproducible builds)

reverts 9f099f3edf

app/build.gradle

@@ -76,8 +76,6 @@ android {
         ndk {
             // abiFilters "armeabi-v7a", "arm64-v8a", "x86", "x86_64"
         }
-
-        buildConfigField "int", "TIMESTAMP", System.currentTimeSeconds().toString()
     }
     bundle {
         language {

app/src/main/java/com/geeksville/mesh/service/MeshService.kt

@@ -907,8 +907,8 @@ class MeshService : Service(), Logging {
     private fun handleReceivedMeshPacket(packet: MeshPacket) {
         if (haveNodeDB) {
             processReceivedMeshPacket(packet.toBuilder().apply {
-                // If the rxTime is invalid (earlier than build time), update with current time
+                // If the rxTime was not set by the device, update with current time
-                if (packet.rxTime < BuildConfig.TIMESTAMP) setRxTime(currentSecond())
+                if (packet.rxTime == 0) setRxTime(currentSecond())
             }.build())
             onNodeDBChanged()
         } else {