Harmonise passing build version

Avoid running some configure step, instead pass it as a define like the Makefile

src/version.cpp

@@ -25,13 +25,6 @@ extern "C" {
 }
 #endif
 
-// This variable is passed via `-D` from the Makefile, but not from CMake
-// (in which `configure_file()` is used on this file to replace some syntax)
-#ifndef BUILD_VERSION_STRING
-    // CMake-specific syntax here
-	#define BUILD_VERSION_STRING "@GIT_REV@"
-#endif
-
 char const *get_package_version_string() {
 	if constexpr (literal_strlen(BUILD_VERSION_STRING) > 0) {
 		return BUILD_VERSION_STRING;