Remove lal...-uninstalled.pc.in pkg-config files

- No longer used by top-level build system
lalsuite_header_links.am: fix bug in header link generation

- When configuring with an absolute path, e.g. /path/to/configure,
  the $^ are also absolute paths to the headers, not relative paths
- In this case, set $targetfile to $file without prepending a path