meson.build: No more CSP_VERSION
meson.build: No more CSP_VERSION

The commit db91837303c24 removed CSP_VERSION form the source tree and
hard coded "version 2" as the default.  No need for compile time
selection now.

Signed-off-by: Yasushi SHOJI <afa9ca3be149447780c2f7b524d61ed3d3db63f9@spacecubics.com>

libcsp/libcsp,libcsp/libcsp