meta-quanta: meta-gsj: Cleanup for Yocto override syntax change

Cleanup with
```
convert-overrides.py meta-quanta/meta-gsj

git grep "_[a-z0-9_/-]*[ :]" -- meta-quanta/meta-gsj

git grep -l _gsj -- meta-quanta/meta-gsj \
  | xargs sed -i 's/_gsj/:gsj/'
```

Note:
Need to revert the change to BBFILE_PATTERN and LAYERSERIES_COMPAT.

After cleanup
```
$ git grep "_[a-z0-9_/-]*[ :]" -- meta-quanta/meta-gsj/ | grep '.bb'
meta-quanta/meta-gsj/recipes-bsp/u-boot/u-boot-fw-utils-nuvoton_%.bbappend:do_install:append:gsj () {
meta-quanta/meta-gsj/recipes-google/ipmi/google-ipmi-sys_%.bbappend:do_install:append:gsj() {
meta-quanta/meta-gsj/recipes-gsj/detect-fan-fail/detect-fan-fail.bb:do_install:append:gsj() {
meta-quanta/meta-gsj/recipes-gsj/quanta-nvme-powerctrl/quanta-nvme-powerctrl.bb:do_install () {
meta-quanta/meta-gsj/recipes-phosphor/fans/phosphor-pid-control_%.bbappend:do_install:append:gsj() {
meta-quanta/meta-gsj/recipes-quanta/network/mac-address_%.bbappend:do_install:append:gsj() {
```

Change-Id: I058371ed32214d665aaaf616a650c2efeaf5be66
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/meta-quanta/meta-gsj/conf/local.conf.sample b/meta-quanta/meta-gsj/conf/local.conf.sample
index eacba35..18e729c 100644
--- a/meta-quanta/meta-gsj/conf/local.conf.sample
+++ b/meta-quanta/meta-gsj/conf/local.conf.sample
@@ -1,11 +1,11 @@
 MACHINE ??= "gsj"
 DISTRO ?= "openbmc-gsj"
 PACKAGE_CLASSES ?= "package_rpm"
-SANITY_TESTED_DISTROS_append ?= " *"
-EXTRA_IMAGE_FEATURES = "debug-tweaks"
-USER_CLASSES ?= "buildstats image-prelink"
+SANITY_TESTED_DISTROS:append ?= " *"
+EXTRA_IMAGE_FEATURES ?= "debug-tweaks"
+USER_CLASSES ?= "buildstats"
 PATCHRESOLVE = "noop"
-BB_DISKMON_DIRS = "\
+BB_DISKMON_DIRS ??= "\
     STOPTASKS,${TMPDIR},1G,100K \
     STOPTASKS,${DL_DIR},1G,100K \
     STOPTASKS,${SSTATE_DIR},1G,100K \