odk: use HTML_TIMESTAMP doxygen option

To be consistent with javadoc, see commit
ac631f9e (odk: use javadoc -notimestamp,
so generated docs don't unnecessarily differ after each build,
2012-10-17).

Change-Id: Ie52d2ca08a873e663869d60413be7bf8ec1e0b56

odk/docs/cpp/Doxyfile

@@ -26,6 +26,7 @@ RECURSIVE = YES
 
 GENERATE_HTML = YES
 HTML_OUTPUT = .
+HTML_TIMESTAMP = NO
 
 GENERATE_LATEX = NO
 

odk/docs/idl/Doxyfile

@@ -15,6 +15,7 @@ RECURSIVE = YES
 
 GENERATE_HTML = YES
 HTML_OUTPUT = .
+HTML_TIMESTAMP = NO
 GENERATE_LATEX = NO
 
 QUIET = %