gdb/arm-tdep.c: Remove "Infinite loop detected" error message.

gdb/arm-tdep.c: Remove "Infinite loop detected" error message.

Since as far back as the beginning of the sourceware repository
the ARM port has printed an error "Infinite loop detected" when
the next_pc calculated is the same as the current one, for example
when encountering a branch to the current PC address.

This causes the test gdb.base/random-signal.exp as the error message
is not expected. I have not been able to find a good reason for the
message to be here so remove it and let the test pass.

gdb/ChangeLog:

2013-11-20  Will Newton  <will.newton@linaro.org>

	* arm-tdep.c (arm_get_next_pc): Remove "Infinite loop detected"
	error message.