selftests/exec: Remove pipe from TEST_GEN_FILES

pipe named FIFO special file is being created in execveat.c to perform
some tests. Makefile doesn't need to do anything with the pipe. When it
isn't found, Makefile generates the following build error:

make: *** No rule to make target
'../tools/testing/selftests/exec/pipe', needed by 'all'.  Stop.

pipe is created and removed during test run-time.

Amended change log to add pipe remove info:
Shuah Khan <skhan@linuxfoundation.org>

Fixes: 61016db ("selftests/exec: Verify execve of non-regular files fail")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: Muhammad Usama Anjum

tools/testing/selftests/exec/Makefile

@@ -5,7 +5,7 @@ CFLAGS += -D_GNU_SOURCE
 
 TEST_PROGS := binfmt_script non-regular
 TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216
-TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir pipe
+TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir
 # Makefile is a run-time dependency, since it's accessed by the execveat test
 TEST_FILES := Makefile