Update Firebase C++ and Unity to use iOS 6.16.0

Built and ran a handful of the iOS testapps on blaze to validate.  Replaced the saved versions of Installations and IID, as the previous frameworks had a reference to a function not available in Xcode 10.3

PiperOrigin-RevId: 293930407

Author: a-maurice

version.sh

@@ -18,9 +18,9 @@
 
 # Used to generate Pod dependencies in the Firebase Unity plugin.
 declare -A POD_SDK_VERSIONS=(
-  ["released"]="6.14.0"  # gen_build.sh: [FIR] Managed by a script. DO NOT EDIT.
-  ["stable"]="6.14.0"  # gen_build.sh: [FIR] Managed by a script. DO NOT EDIT.
-  ["head"]="6.14.0"  # gen_build.sh: [FIR] Managed by a script. DO NOT EDIT.
+  ["released"]="6.16.0"  # gen_build.sh: [FIR] Managed by a script. DO NOT EDIT.
+  ["stable"]="6.16.0"  # gen_build.sh: [FIR] Managed by a script. DO NOT EDIT.
+  ["head"]="6.16.0"  # gen_build.sh: [FIR] Managed by a script. DO NOT EDIT.
 )
 
 help() {