Remove unused defines

src/config.in.hpp

@@ -60,9 +60,6 @@
 /* Defined to 1 if the underlying system provides the strtof function. */
 #cmakedefine HAVE_STRTOF 1
 
-/* Defined to 1 if the underlying system provides the M_PI constant. */
-#cmakedefine HAVE_M_PI 1
-
 /* Defined to 1 if the underlying system provides the posix_fadvise function. */
 #cmakedefine HAVE_POSIX_FADVISE 1
 
@@ -148,11 +145,6 @@ typedef std::make_signed<size_t>::type ssize_t;
 inline float strtof( const char *s, char **se ) { return (float) strtod( s, se ); }
 #endif
 
-#if !defined(HAVE_M_PI)
-/* This is only called if the math header files don't include it: stating it here is fine. */
-#define M_PI 3.1415926535897932384626433832795
-#endif
-
 /* Define standard endianness macros, if they're missing. */
 #if defined(HAVE_ENDIAN_H)
 #include <endian.h>