ANDROID: export: Disable symbol trimming on modules

Trimming non-whitelisted symbols from modules will be useful once we
introduce GKI modules, but in the meantime it causes pain downstream for
out-of-tree modules as vendors will have to whitelist the symbols they
need.

The right solution would be to apply the trimming or not to a module
based on an explicit list of GKI modules, but as we currently don't have
any (nor we have a good way to differentiate them in the kernel build
system), let's simply disable the trimming for all modules altogether,
and get things unblocked for GKI 1.0.

Bug: 148277666
Signed-off-by: Quentin Perret <qperret@google.com>
Change-Id: I2513d85c46eefc62c59883b724b6153dd27b3671