[apps/continuous_function] Cut clearCache method

Inlined call to ContinuousFunction::clearCache and removed the method,
as its name was confusing.

Change-Id: I54454fb0b06167e01249afaa5b23932451125f2e

apps/shared/continuous_function.cpp

@@ -125,7 +125,7 @@ void ContinuousFunction::setPlotType(PlotType newPlotType, Poincare::Preferences
 
   recordData()->setPlotType(newPlotType);
 
-  clearCache();
+  setCache(nullptr);
 
   // Recompute the layouts
   m_model.tidy();
@@ -253,12 +253,12 @@ float ContinuousFunction::tMax() const {
 
 void ContinuousFunction::setTMin(float tMin) {
   recordData()->setTMin(tMin);
-  clearCache();
+  setCache(nullptr);
 }
 
 void ContinuousFunction::setTMax(float tMax) {
   recordData()->setTMax(tMax);
-  clearCache();
+  setCache(nullptr);
 }
 
 void * ContinuousFunction::Model::expressionAddress(const Ion::Storage::Record * record) const {
@@ -352,7 +352,7 @@ Poincare::Expression ContinuousFunction::sumBetweenBounds(double start, double e
 }
 
 Ion::Storage::Record::ErrorStatus ContinuousFunction::setContent(const char * c, Poincare::Context * context) {
-  clearCache();
+  setCache(nullptr);
   return ExpressionModelHandle::setContent(c, context);
 }
 

apps/shared/continuous_function.h

@@ -82,7 +82,6 @@ public:
   // Cache
   ContinuousFunctionCache * cache() const { return m_cache; }
   void setCache(ContinuousFunctionCache * v) { m_cache = v; }
-  void clearCache() { m_cache = nullptr; }
   Ion::Storage::Record::ErrorStatus setContent(const char * c, Poincare::Context * context) override;
 private:
   constexpr static float k_polarParamRangeSearchNumberOfPoints = 100.0f; // This is ad hoc, no special justification

apps/shared/continuous_function_cache.cpp

@@ -24,7 +24,7 @@ void ContinuousFunctionCache::PrepareForCaching(void * fun, ContinuousFunctionCa
      * by 1 for cache hits. As an added safety, we add another buffer of
      * k_cacheHitTolerance, raising the threshold for caching to three times
      * the tolerance. */
-    function->clearCache();
+    function->setCache(nullptr);
     return;
   }
   if (function->cache() != cache) {