m32r: Remove unused .altinstructions and .exit.* code from linker script.

It appears that m32r copied the .altinstructions definition from x86
when the architecture was first merged into Linux.  m32r doesn't put
anything in .altinstructions, so this is just dead code.

The following block affecting .exit.text/.exit.data, which has a
comment also copied from x86, should also be deleted; the linker
script later discards the .exit.text and .exit.data sections.

Signed-off-by: Tim Abbott <tabbott@ksplice.com>
Signed-off-by: Hirokazu Takata <takata@linux-m32r.org>