Sort rblf_wildcard results and remove file existence functions

Kati's $(wildcard) results are guaranteed to be sorted,
but go's filepath.Glob() is not.

Remove the file existence functions because they can
just be replaced with wildcards.

Bug: 226974242
Test: go test
Change-Id: I02fb6292b932bc28cd856ec3c7cb9ed9e96ca630
diff --git a/tools/rbcrun/testdata/module1.star b/tools/rbcrun/testdata/module1.star
index 913fb7d..be04f75 100644
--- a/tools/rbcrun/testdata/module1.star
+++ b/tools/rbcrun/testdata/module1.star
@@ -2,6 +2,6 @@
 load("assert.star", "assert")
 
 # Make sure that builtins are defined for the loaded module, too
-assert.true(rblf_file_exists("module1.star"))
-assert.true(not rblf_file_exists("no_such file"))
+assert.true(rblf_wildcard("module1.star"))
+assert.true(not rblf_wildcard("no_such file"))
 test = "module1"