In 1.24, installedPkgs contained only references to the external package
database, not any internal libraries. In particular, when we built a
dynamically linked executable, installedPkgs did NOT have a reference to
the internal library; instead, depLibraryPaths has a special case
(hasInternalDeps) to add the final libdir to the RPATH.

In HEAD, after 0d15edef

, we started adding internal libraries (with the
INPLACE registrations) to installedPkgs to fix #2971.  But depLibraryPaths
was not updated, which means that the inplace registrations got picked
up and added to the RPATH, resulting in bad temporary directories
showing up in RPATHs.

In this commit, we just filter out internal entries from installedPkgs
and compute the library dirs for them from scratch (this code already
existed, so no loss!)

Fixes #4025.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>