[gdb/tdep] Remove includes of gdbsupport/common-defs.h

In commit 18d2988e5da ("gdb, gdbserver, gdbsupport: remove includes of early
headers") all includes of gdbsupport/common-defs.h where removed, but
commit c1cdee0e2c1 ("gdb: LoongArch: Add support for hardware watchpoint")
reintroduced some.

Fix this by removing them.

Tested by doing this on x86_64-linux:
...
$ make \
    nat/loongarch-hw-point.o \
    nat/loongarch-linux.o \
    nat/loongarch-linux-hw-point.o
  CXX    nat/loongarch-hw-point.o
  CXX    nat/loongarch-linux.o
  CXX    nat/loongarch-linux-hw-point.o
...

Approved-By: Simon Marchi <simon.marchi@efficios.com>