Remove obsolete llndk_library

Remove llndk_library in favor of cc_library with llndk.symbol_file.

Bug: 170784825
Test: m checkbuild
Test: TestLlndkLibrary
Change-Id: I43580976589a7a2a176d7442be53fa043c0c8324

cc/cc.go

@@ -1121,13 +1121,6 @@ func (c *Module) IsLlndkPublic() bool {
 	return c.VendorProperties.IsLLNDK && !c.VendorProperties.IsVNDKPrivate
 }
 
-func (c *Module) IsLlndkLibrary() bool {
-	if _, ok := c.linker.(*llndkStubDecorator); ok {
-		return true
-	}
-	return false
-}
-
 func (m *Module) NeedsLlndkVariants() bool {
 	lib := moduleLibraryInterface(m)
 	return lib != nil && (lib.hasLLNDKStubs() || lib.hasLLNDKHeaders())