Revert "[FileCheck] Fix parsing empty global and pseudo variable names" (#83657)

Reverts #82595

See build failure
https://lab.llvm.org/buildbot/#/builders/139/builds/60549

Author: kovdan01

llvm/lib/FileCheck/FileCheck.cpp

@@ -297,12 +297,6 @@ Pattern::parseVariable(StringRef &Str, const SourceMgr &SM) {
   if (Str[0] == '$' || IsPseudo)
     ++I;
 
-  if (I == Str.size())
-    return ErrorDiagnostic::get(SM, Str.slice(I, StringRef::npos),
-                                StringRef("empty ") +
-                                    (IsPseudo ? "pseudo " : "global ") +
-                                    "variable name");
-
   if (!isValidVarNameStart(Str[I++]))
     return ErrorDiagnostic::get(SM, Str, "invalid variable name");