Process metadata only in metadata.cpp

Improves cache utilization as fewer things are passed via CFLAGS to
all files.  In the event that no metadata is available, let the cpp
file handle warning about default usage.

platformio.ini

@@ -110,8 +110,7 @@ ldscript_4m1m = eagle.flash.4m1m.ld
 
 [scripts_defaults]
 extra_scripts =
-  pre:pio-scripts/set_version.py
-  pre:pio-scripts/set_repo.py
+  pre:pio-scripts/set_metadata.py
   post:pio-scripts/output_bins.py
   post:pio-scripts/strip-floats.py
   pre:pio-scripts/user_config_copy.py