soc/arm/ti_lm3s6965: remove unnecessary extern C block

This header doesn't define any symbols with linkage.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

soc/arm/ti_lm3s6965/soc.h

@@ -17,10 +17,6 @@
 
 #include <sys/util.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /* default system clock */
 
 #define SYSCLK_DEFAULT_IOSC_HZ MHZ(12)
@@ -77,8 +73,4 @@ extern "C" {
 
 #endif /* !_ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _BOARD__H_ */