E3-1132: Remove record search from expandDBD

See https://github.com/paulscherrerinstitute/require/commit/134aed5a5e618ae12a95134862401f1dcc92c834 for some context. Instead of searching recursively through .dbd files, one can instead just filter source files for %Record.(c|cc|cpp). This simplifies the special python/tcl/pl script to handle dbd files.