[One .NET] Do not always preserve Android.Runtime.CharSequence (#5363)

Context: #5167

The `Android.Runtime.CharSequence` type is not accessed via reflection.

Allowing `CharSequence` to be linked allows unreferenced members to
be removed by the linker (yay!), e.g. when comparing the `.apk` built
from the `BuildReleaseArm64False` test:

	$ apkdiff before.apk after.apk
	…
	Type Android.Runtime.CharSequence
	  -             Method public static SIGERR ToLocalJniHandle (System.Collections.Generic.IEnumerable`1<char>)
	…

The `Android.Runtime.CharSequence.ToLocalJniHandle()` is removed.

src/Microsoft.Android.Sdk.ILLink/PreserveLists/Mono.Android.xml

@@ -3,7 +3,6 @@
 	<assembly fullname="Mono.Android">
 		<type fullname="Android.Runtime.AndroidEnvironment" />
 		<type fullname="Android.Runtime.AnnotationAttribute" />
-		<type fullname="Android.Runtime.CharSequence" />
 		<type fullname="Android.Runtime.ConstructorBuilder" />
 		<type fullname="Android.Runtime.GeneratedDummyHost" />
 		<type fullname="Android.Runtime.GeneratedEnumAttribute" />