Remove unnecessary [[maybe_unused]].

We started actually using fContext within this class at
http://review.skia.org/445296.

Change-Id: I1e9e36e6177e6b0eba71a8486e50956d112e276e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/445638
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

src/sksl/SkSLAnalysis.cpp

@@ -764,7 +764,7 @@ bool Analysis::CheckProgramUnrolledSize(const Program& program) {
     private:
         using INHERITED = ProgramVisitor;
 
-        [[maybe_unused]] const Context& fContext;
+        const Context& fContext;
         int fFunctionSize = 0;
         int fUnrollFactor = 1;
         std::unordered_map<const FunctionDeclaration*, int> fFunctionCostMap;