cleanup: move definition of get_units() to core/unit.c

The function is declared in core/unit.h, therefore it seems logical
to define it in the corresponding source file.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/subsurfacestartup.c

@@ -110,11 +110,6 @@ int quit, force_root, ignore_bt;
 char *testqml = NULL;
 #endif
 
-const struct units *get_units()
-{
-	return &prefs.units;
-}
-
 /*
  * track whether we switched to importing dives
  */

core/units.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "units.h"
 #include "gettext.h"
+#include "pref.h"
 
 int get_pressure_units(int mb, const char **units)
 {
@@ -168,3 +169,8 @@ double get_weight_units(unsigned int grams, int *frac, const char **units)
 		*units = unit;
 	return value;
 }
+
+const struct units *get_units()
+{
+	return &prefs.units;
+}