selftests: remove obsolete build restriction for gpio

Build restrictions related to the gpio-mockup-chardev helper are
no longer relevant so remove them.

Signed-off-by: Kent Gibson <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>
Signed-off-by: Bartosz Golaszewski <[e-mail]>

tools/testing/selftests/Makefile

···
 export KSFT_KHDR_INSTALL_DONE := 1
 export BUILD
 
-# build and run gpio when output directory is the src dir.
-# gpio has dependency on tools/gpio and builds tools/gpio
-# objects in the src directory in all cases making the src
-# repo dirty even when objects are relocated.
-ifneq (1,$(DEFAULT_INSTALL_HDR_PATH))
-	TMP := $(filter-out gpio, $(TARGETS))
-	TARGETS := $(TMP)
-endif
-
 # set default goal to all, so make without a target runs all, even when
 # all isn't the first target in the file.
 .DEFAULT_GOAL := all