libdm: Remove dm_linear_fuzzer.

This fuzzer can only mutate the numerical inputs to a dm-linear table,
which is unlikely to find kernel bugs, and very unlikely to find libdm
bugs. There are a number of automated notifications from it due to
making ASSERT_EQ a no-op, which causes misuse of libdm API calls. None
of these appear to be real bugs.

Bug: 174907083
Test: N/A
Change-Id: Iaa8955eaa4423e4315b8cb74741e6425a56cc303