[FP] Do not assert that model has shared term (#7585)

[FP] Do not assert that model has shared term (#7585)

Fixes #7569. Currently, the FP solver asserts that
m->hasTerm(sharedTerm) is always true for the real term in the
conversion from real to floating-point value. This is not necessarily
the case because the arithmetic solver computes values for the variables
in the shared terms but not necessarily for the terms themselves. This
commit removes the assertion and instead relies on the fact that a later
assertion checks that m->getValue(sharedTerm).isConst(), which is the
property that we are actually interested in.