sagemathgh-38915: Remove register macro in Ginac

    
Fixes
```
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14
.41.34120\include\xkeycheck.h(341): warning C4005: 'register': macro
redefinition
../src/sage/symbolic/ginac/constant.cpp(23): note: see previous
definition of 'register'
C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14
.41.34120\include\xkeycheck.h(343): fatal error C1189: #error:  The C++
Standard Library forbids macroizing the keyword "register". Enable
warning C4005 to find the forbidden define.
```

Not sure why `register` was declared there in the first place.

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URL: sagemath#38915
Reported by: Tobias Diez
Reviewer(s): Travis Scrimshaw

src/sage/symbolic/ginac/constant.cpp

@@ -20,7 +20,6 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#define register
 #include <Python.h>
 #include "py_funcs.h"
 #include "constant.h"

src/sage/symbolic/ginac/ex.cpp

@@ -20,7 +20,6 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#define register
 #include <Python.h>
 #include "ex.h"
 #include "ex_utils.h"

src/sage/symbolic/ginac/fderivative.cpp

@@ -20,7 +20,6 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#define register
 #include <Python.h>
 #include "py_funcs.h"
 #include "fderivative.h"

src/sage/symbolic/ginac/function.cpp

@@ -20,7 +20,6 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#define register
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "py_funcs.h"

src/sage/symbolic/ginac/inifcns_hyperg.cpp

@@ -23,7 +23,6 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#define register
 #include <Python.h>
 #include "py_funcs.h"
 #include "inifcns.h"

src/sage/symbolic/ginac/numeric.cpp

@@ -49,7 +49,6 @@
  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
-#define register
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include "flint/fmpz.h"