cmGeneratorTarget: Remove unnecessary target type check in dependency tracing

Since commit 2600e923a6 (Disallow INTERFACE libraries with
add_custom_command(TARGET)., 2014-03-19, v3.0.0-rc3~1^2), we do not
trace dependencies of INTERFACE libraries that do not participate in the
build system.  Therefore we can remove a check of the target type from
the implementation that had been added by commit 9db9c1fc8b (cmTarget:
Don't try to get sources of an INTERFACE_LIBRARY., 2014-02-14,
v3.0.0-rc1~20^2).
1 file changed