BUG: Revert "ENH: enable unaligned loads on x86"

This reverts commit aef286debfd11a62f1c337dea55624cee7fd4d9e.
x86 platform works with unaligned access but the compiler is allowed to assume
all data is aligned to its size by the C standard. This means it can vectorize
instructions peeling only by the size of the type, if the data is not aligned
to this size one ends up with data not correctly aligned for SSE instructions
(16 byte).
So this flag can only be enabled if autovectorization is disabled.