Remove extended precision JPRH

[samhatfield]

JPRH (the extended floating point type exported by Fiat here) is referenced in a few places in ecTrans. E.g.:

• SULEG
• PRE_SULEG_MOD (not actually used)
• SUGAW

JPRH is actually always the same as JPRD in Fiat. It's only equal to the extended type when REALHUGE is defined. But there is no way to set this when building Fiat, so it looks like a half-deprecated feature.

Whether we keep this in Fiat is another issue, but for now perhaps we should delete all references to JPRH and replace with JPRD, since this is what we are actually doing.

@wdeconinck's upcoming PR #61 effectively does this in SUGAW anyway.