Remove HIDE_SYMBOLS_BY_DEFAULT: replace by a default configuration in gz-cmake. (#399)

See gazebosim/gz-cmake#166 (comment)

Signed-off-by: Jose Luis Rivero <jrivero@osrfoundation.org>

Author: j-rivero

CMakeLists.txt

@@ -75,8 +75,7 @@ set (GZ_TOOLS_VER 2)
 #============================================================================
 # Configure the build
 #============================================================================
-gz_configure_build(QUIT_IF_BUILD_ERRORS
-  HIDE_SYMBOLS_BY_DEFAULT)
+gz_configure_build(QUIT_IF_BUILD_ERRORS)
 
 #============================================================================
 # gz command line support