doc: remove warning with Doxygen 1.9.7

[ upstream commit 6df586f544d90f1eb266d75e6c8215e1c081019c ]

Since doxygen 1.9.7 version, HTML_TIMESTAMP configuration option
changed to TIMESTAMP [2]. Fixed the following warning[1] by
removing TIMESTAMP options all together as all new versions(since 1.8.9)
of doxygen this option is disabled by default. Another option was
considered to have this configuration option based on version check, which
may not be worth having it, especially, external_program.version()
API introduced in 0.62.0 version of meson.

[1]
Warning: Tag 'HTML_TIMESTAMP' at line 115 of file 'doc/api/doxy-api.conf'
has become obsolete.

[2]
https://www.doxygen.nl/manual/config.html#cfg_timestamp

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

doc/api/doxy-api.conf.in

@@ -100,7 +100,6 @@ GENERATE_DEPRECATEDLIST = YES
 VERBATIM_HEADERS        = NO
 ALPHABETICAL_INDEX      = NO
 
-HTML_TIMESTAMP          = NO
 HTML_DYNAMIC_SECTIONS   = YES
 SEARCHENGINE            = YES
 SORT_MEMBER_DOCS        = NO