Remove export static DH ciphersuites

Remove support for the two export grade static DH ciphersuites. These two
ciphersuites were newly added (along with a number of other static DH
ciphersuites) to 1.0.2. However the two export ones have *never* worked
since they were introduced. It seems strange in any case to be adding new
export ciphersuites, and given "logjam" it also does not seem correct to
fix them.

Reviewed-by: Richard Levitte <levitte@openssl.org>