Don't remove files copied to host

Nowadays, if we do in-tree build and run tests sequentially, some source
files are removed, due to the following pattern:

set pi_txt [gdb_remote_download host ${srcdir}/${subdir}/pi.txt]

remote_exec host "rm -f $pi_txt"

If testing is run sequentially, file ${srcdir}/${subdir}/pi.txt is
copied to ${objdir}/${subdir}/pi.txt.  However, ${objdir} is ${srcdir}
in the in-tree build/test, so the file is coped to itself, as a nop.
As a result, the file in source is removed at the end of test.

This patch fixes this problem by not removing files copied to host in
each test.  This patch also addresses the question we've had that why
don't we keep files copied to host because they are needed to reproduce
certain fails.

gdb/testsuite:

2014-10-20  Yao Qi  <yao@codesourcery.com>

	* gdb.base/checkpoint.exp: Don't remove file copied on host.
	* gdb.base/step-line.exp: Likewise.
	* gdb.dwarf2/dw2-anonymous-func.exp: Likewise.
	* gdb.dwarf2/dw2-basic.exp: Likewise.
	* gdb.dwarf2/dw2-compressed.exp: Likewise.
	* gdb.dwarf2/dw2-filename.exp: Likewise.
	* gdb.dwarf2/dw2-intercu.exp: Likewise.
	* gdb.dwarf2/dw2-intermix.exp: Likewise.
	* gdb.dwarf2/dw2-producer.exp: Likewise.
	* gdb.dwarf2/mac-fileno.exp: Likewise.
	* gdb.python/py-frame-args.exp: Likewise.
	* gdb.python/py-framefilter.exp: Likewise.
	* gdb.python/py-mi.exp: Likewise.
	* gdb.python/py-objfile-script.exp: Likewise
	* gdb.python/py-pp-integral.exp: Likewise.
	* gdb.python/py-pp-re-notag.exp: Likewise.
	* gdb.python/py-prettyprint.exp: Likewise.
	* gdb.python/py-section-script.exp: Likewise.
	* gdb.python/py-typeprint.exp: Likewise.
	* gdb.python/py-xmethods.exp: Likewise.
	* gdb.stabs/weird.exp: Likewise.
	* gdb.xml/tdesc-regs.exp: Likewise.

gdb/testsuite/gdb.python/py-section-script.exp

@@ -72,5 +72,3 @@ gdb_test "b [gdb_get_line_number {break to inspect} ${testfile}.c ]" \
 gdb_test "continue" ".*Breakpoint.*"
 
 gdb_test "print ss" " = a=<1> b=<2>"
-
-remote_file host delete ${remote_python_file}