libxenguest: drop now unused le32_to_cpup() from lz4 decompression

libxenguest: drop now unused le32_to_cpup() from lz4 decompression

While gcc doesn't warn about this because of it being static inline,
clang does, causing the build to fail there because of -Werror.

Fixes: d8099d94dfaa ("libxenguest: add get_unaligned_le32()")
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>