MAINTAINERS: drop broken reference to i2c/trivial-devices

Due to RST rework, the reference to i2c/trivial-devices was changed, but the
result is broken. However, let's just drop the whole reference, since it
doesn't make sense in the first place to reference this "global" file
for a single driver.

Fixes: 8c27ceff ("docs: fix locations of several documents that got moved")
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: Kevin Tsai <ktsai@capellamicro.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>