apexer: remove --do_not_check_keyname

Since fe4ff29b4d47fa8ae242fb7e084215d3afada4b5 (in system/apex), apexer
doesn't check keyname (--key vs --manifest.name). So, passing
--do_not_check_keyname doesn't make any sense.

This is a preparation to remove (or deprecate) "apex_name" property from
"apex" module.

Bug: 267581665
Test: m
Change-Id: I3737d1e36d305375a523a23a6bbeb2d23586e578

apex/apex_test.go

@@ -4138,8 +4138,6 @@ func TestApexName(t *testing.T) {
 	module := ctx.ModuleForTests("myapex", "android_common_com.android.myapex_image")
 	apexManifestRule := module.Rule("apexManifestRule")
 	ensureContains(t, apexManifestRule.Args["opt"], "-v name com.android.myapex")
-	apexRule := module.Rule("apexRule")
-	ensureContains(t, apexRule.Args["opt_flags"], "--do_not_check_keyname")
 
 	apexBundle := module.Module().(*apexBundle)
 	data := android.AndroidMkDataForTest(t, ctx, apexBundle)