Remove Forcing Diagnostic Colours from CMakeLists.txt (#1597)

Fixes https://github.com/harfbuzz/harfbuzz/issues/1596

CMakeLists.txt

@@ -842,18 +842,6 @@ if (NOT SKIP_INSTALL_LIBRARIES AND NOT SKIP_INSTALL_ALL)
   endif ()
 endif ()
 
-if (UNIX AND CMAKE_GENERATOR STREQUAL "Ninja")
-  if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fcolor-diagnostics")
-    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fcolor-diagnostics")
-  endif ()
-  if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fdiagnostics-color")
-    set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fdiagnostics-color")
-  endif ()
-endif ()
-
-
 if (HB_BUILD_TESTS)
   ## src/ executables
   foreach (prog main test test-would-substitute test-size-params test-buffer-serialize hb-ot-tag test-unicode-ranges)