[gdb/testsuite] Fix gdb.dwarf2/imported-unit-bp-c.exp for remote host

Fix test-case gdb.dwarf2/imported-unit-bp-c.exp on remote by removing a
downloaded source file.

Tested on x86_64-linux.

gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp.tcl

diff --git a/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp.tcl b/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp.tcl
index 6bef2bd..62dee7d 100644
--- a/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp.tcl
+++ b/gdb/testsuite/gdb.dwarf2/imported-unit-bp.exp.tcl
@@ -122,5 +122,10 @@
 
 gdb_reinitialize_dir /tmp
 
+# Compilation on remote host downloads the source files to remote host, but
+# doesn't clean them up, allowing gdb to find $srcfile, in contrast to
+# non-remote host.
+remote_file host delete $srcfile
+
 # Using an absolute path is important to see the bug.
 gdb_test "break /tmp/${srcfile}:19" "Breakpoint .* file $srcfile, line .*"