Build/CMake: disable unity builds for external dependencies as their support for unity builds was rather hacky and relied too much on random factors

dep/bzip2/CMakeLists.txt

@@ -41,12 +41,3 @@ else()
       FOLDER
         "dep")
 endif()
-
-if(UNITY_BUILDS)
-  set_target_properties(bzip2
-      PROPERTIES UNITY_BUILD ON)
-  set_target_properties(bzip2
-      PROPERTIES
-        UNITY_BUILD_MODE BATCH
-        UNITY_BUILD_BATCH_SIZE 8)
-endif()