Remove default sizeof sizes in configure script when cross-compiling

Remove default sizeof sizes in configure script when cross-compiling

Since version 2.50 autoconf fully supports checking sizes of types
(with AC_CHECK_SIZEOF) when cross-compiling.  Therefore there is no
need to preset the respective cache variables anymore.  The following
patch removes the special case.  There is no need to adjust AC_PREREQ
as it's set to 2.50 already.

Tested successfully cross-building for the mips64el-linux-gnu host on
an i386-linux-gnu build system, removing the following warning
(because of a mismatch for the "long" type):

Sizeof(__U64__TYPEDEF) is 4 should be 8
Problem detected with asm_types.h

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>