scripts/find-unused-docs: Fix massive false positives

scripts/find-unused-docs.sh invokes scripts/kernel-doc to find out if a
source file contains kerneldoc or not.

However, as it passes the no longer supported "-text" option to
scripts/kernel-doc, the latter prints out its help text, causing all
files to be considered containing kerneldoc.

Get rid of these false positives by removing the no longer supported
"-text" option from the scripts/kernel-doc invocation.

Cc: stable@vger.kernel.org  # 4.16+
Fixes: b0514267 ("scripts: kernel-doc: get rid of unused output formats")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200127093107.26401-1-geert+renesas@glider.be


Signed-off-by: Jonathan Corbet <corbet@lwn.net>