build: drop superfluous HAVE_BUILD_INFO define

build.h should always be generated before clientversion.cpp is compiled
due to the following explicit dependency in src/CMakeLists.txt:

add_dependencies(bitcoin_clientversion generate_build_info)

Hence there is no need to gate the inclusion of that header with an
extra define.

src/CMakeLists.txt

@@ -17,10 +17,6 @@ add_custom_target(generate_build_info
 add_library(bitcoin_clientversion OBJECT EXCLUDE_FROM_ALL
   clientversion.cpp
 )
-target_compile_definitions(bitcoin_clientversion
-  PRIVATE
-    HAVE_BUILD_INFO
-)
 target_link_libraries(bitcoin_clientversion
   PRIVATE
     core_interface

src/clientversion.cpp

@@ -23,14 +23,12 @@ using util::Join;
 const std::string CLIENT_NAME("Satoshi");
 
 
-#ifdef HAVE_BUILD_INFO
 #include <build.h>
 // The <build.h>, which is generated by the build environment (cmake/script/GenerateBuildInfo.cmake),
 // could contain only one line of the following:
 //   - "#define BUILD_GIT_TAG ...", if the top commit is tagged
 //   - "#define BUILD_GIT_COMMIT ...", if the top commit is not tagged
 //   - "// No build information available", if proper git information is not available
-#endif
 
 //! git will put "#define GIT_COMMIT_ID ..." on the next line inside archives. $Format:%n#define GIT_COMMIT_ID "%H"$