[gdb/testsuite] Remove superfluous pid in temp files

[gdb/testsuite] Remove superfluous pid in temp files

While trying to use gdb_can_simple_compile with a d program, I ran into:
...
/data/vries/gdb/f37/build/gdb/testsuite/temp/105856/can_compile_d-105856.d: \
  error: module 'can_compile_d-105856' has non-identifier characters in \
  filename, use module declaration instead
...

The d compiler has a problem with the filename can_compile_d-105856.d, which
contains the pid.  The pid is added by gdb_simple_compile:
...
    set obj [standard_temp_file $name-[pid].$postfix]
...
but it's unnecessary because standard_temp_file already uses the pid.

Fix this by removing "[pid]" in all calls to standard_temp_file.

Tested on x86_64-linux.