lib/uuid: remove conflicting Windows implementation of gettimeofday()

lib/uuid: remove conflicting Windows implementation of gettimeofday()

When building libuuid for Windows with MinGW with the default settings,
there is a build error in lib/uuid/gen_uuid.c because the explicit
definition of gettimeofday() conflicts with MinGW's declaration of
gettimeofday().  gen_uuid.c apparently expects USE_MINGW to be defined
to avoid that, but the build system doesn't actually do that.

Since native Windows builds of e2fsprogs are currently only supported
via MinGW anyway (in particular, Visual Studio is not supported), let's
fix this by just removing our own definition of gettimeofday().

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>