res_pjsip: Remove spurious error logging when printing silent headers

Asterisk patched the pjproject source to avoid crashing when pjproject
sip_msg headers are encountered with NULL vptr's, but the patch also
output error messages for some valid headers which simply did not need
to be added to the message itself, such as hidden route headers.

pjproject has since applied a similar patch to their baseline to avoid
crashes, but their version also avoids the spurious error logging.

Lets use their patch instead.

ASTERISK-27961 #close

Change-Id: I2ddbd82c8da10e0dcc9807a48089d1f3c2d6e389