bitbake: data_smart: Ensure _remove operations on newly set variables are cleared

We clear append/prepend on newly set variables, we should also clear
remove operations. If we don't do this, there is no way we can actually
delete a remove operation. Bitbake internally uses parsing=True to avoid
these side effects when making its own internal calls.

Also add a testcase to bitbake-selftest to ensure we remain consistent going
forward from here.

(Bitbake rev: 3a319f079d699c870d8531e051ab65e6278d1fa5)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/data_smart.py

@@ -546,6 +546,8 @@ class DataSmart(MutableMapping):
                 del self.dict[var]["_append"]
             if "_prepend" in self.dict[var]:
                 del self.dict[var]["_prepend"]
+            if "_remove" in self.dict[var]:
+                del self.dict[var]["_remove"]
             if var in self.overridedata:
                 active = []
                 self.need_overrides()