remove old dlstart stage-2 symbolic lookup code; add new generic

remove old dlstart stage-2 symbolic lookup code; add new generic

this new generic version of the stage-2 function lookup should work
for any arch where static data is accessible via got-relative or
pc-relative addressing, using approximately the technique described in
the log message for commit 2907afb8dbd4c1d34825c3c9bd2b41564baca210.

since all the mips-like archs that need got slots fo access static
data have already transitioned to the new stage chaining scheme, the
old dynamic symbol lookup code is now removed.

aarch64, arm, and sh have not yet transitioned; with this commit, they
are now using the new generic code.