ti-ipc-rtos: cannot directly depend on doxygen here

There's no doxygen recipe provided by meta-ti, nor oe-core. And meta-ti
expects doxygen to be available as a host tool, per layers.conf

Signed-off-by: Denys Dmytriyenko <denys@ti.com>

recipes-ti/ipc/ti-ipc-rtos_git.bb

@@ -2,7 +2,7 @@ require ti-ipc.inc
 require ti-ipc-common.inc
 require ti-ipc-rtos.inc
 
-DEPENDS = "ti-xdctools ti-sysbios doxygen-native zip-native"
+DEPENDS = "ti-xdctools ti-sysbios zip-native"
 
 PACKAGES =+ "${PN}-fw"
 FILES_${PN}-fw = "${base_libdir}/firmware/*"