dahdi-tools: clean up make flags, remove $(FPIC)

dahdi-tools: clean up make flags, remove $(FPIC)

- Remove all flags/variables that are not used at all.

- dahdi-tools already makes sure that the compiler emits
  position-independent code for libtonezone. Adding $(FPIC) makes no
  difference. In addition the dahdi-toolsbuild system puts its own flag
  behind the CFLAGS, overriding whatever was set before. Also the
  applications should never be built with PIC, it should only be done for
  the lib.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>