Finish converting GSL to absl::Span

One less dependency.

Change-Id: Iaac25a3c1312a21a8a2b77b8cfee2463bdb51196
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/motors/print/semihosting.h b/motors/print/semihosting.h
index 6ea6c3b..d323a7a 100644
--- a/motors/print/semihosting.h
+++ b/motors/print/semihosting.h
@@ -1,6 +1,7 @@
 #ifndef MOTORS_PRINT_SEMIHOSTING_H_
 #define MOTORS_PRINT_SEMIHOSTING_H_
 
+#include "absl/types/span.h"
 #include "motors/print/print.h"
 
 namespace frc971 {
@@ -23,7 +24,7 @@
 
   void Initialize() override {}
 
-  int WriteStdout(gsl::span<const char> buffer) override;
+  int WriteStdout(absl::Span<const char> buffer) override;
 
   // Could easily implement an optional WriteDebug which goes to a separate
   // file if the name is filled out in the parameters.