Move strace -m/explicit location test to strace.exp

Move strace -m/explicit location test to strace.exp

One of the build slaves shows this error running explicit.exp:

(gdb) strace -m gdbfoobarbaz
Remote failure reply: E.In-process agent library not loaded in process.
Fast and static tracepoints unavailable.
(gdb) FAIL: gdb.linespec/explicit.exp: strace -m gdbfoobarbaz

There are two big problems with this test:
1) The expected output is actually not what the test is meant to test for.
2) This test should really only run where it is supported.

This is most easily fixed by moving the test to gdb.trace/strace.exp.

gdb/testsuite/ChangeLog

	* gdb.linespec/explicit.exp: Move strace test from here ...
	* gdb.trace/strace.exp: ... to here.