doc: Drop tests/kernel from doxygen input path

We are running into a doxygen error with intmath.c from
tests/kernel/common/src/.

intmath.c:29: warning: member with no name found.

Drop tests/kernel from the doxygen input path for now.

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

doc/zephyr.doxyfile.in

@@ -756,8 +756,7 @@ INPUT                  = @ZEPHYR_BASE@/include/ \
                          @ZEPHYR_BASE@/include/arch/nios2/ \
                          @ZEPHYR_BASE@/lib/libc/minimal/include/ \
                          @ZEPHYR_BASE@/include/net/dns_resolve.h \
-			 @ZEPHYR_BASE@/subsys/testsuite/ztest/include/ \
-			 @ZEPHYR_BASE@/tests/kernel/
+			 @ZEPHYR_BASE@/subsys/testsuite/ztest/include/
 
 # This tag can be used to specify the character encoding of the source files
 # that doxygen parses. Internally doxygen uses the UTF-8 encoding. Doxygen uses