mesa: remove unused isblank() function

Reviewed-by: Matt Turner <mattst88@gmail.com>

src/mesa/main/imports.h

@@ -92,7 +92,6 @@ typedef union { GLfloat f; GLint i; GLuint u; } fi_type;
 
 #if defined(_MSC_VER)
 #if _MSC_VER < 1800  /* Not req'd on VS2013 and above */
-static inline int isblank(int ch) { return ch == ' ' || ch == '\t'; }
 #define strtoll(p, e, b) _strtoi64(p, e, b)
 #endif /* _MSC_VER < 1800 */
 #define strcasecmp(s1, s2) _stricmp(s1, s2)