Revert "Move static const assignment to MDCTextControl.m (#9701)"

This reverts commit 2d8d6a082fbf046df5b108b03e4566fb1fe91ea8.

components/private/TextControlsPrivate/src/Shared/MDCTextControl.h

diff --git a/components/private/TextControlsPrivate/src/Shared/MDCTextControl.h b/components/private/TextControlsPrivate/src/Shared/MDCTextControl.h
index 7894468..2080657 100644
--- a/components/private/TextControlsPrivate/src/Shared/MDCTextControl.h
+++ b/components/private/TextControlsPrivate/src/Shared/MDCTextControl.h
@@ -23,6 +23,10 @@
 #import "MDCTextControlState.h"
 #import "MDCTextControlVerticalPositioningReference.h"
 
+static inline UIFont *_Nonnull MDCTextControlDefaultUITextFieldFont() {
+  return [UIFont preferredFontForTextStyle:UIFontTextStyleBody];
+}
+
 static const CGFloat kMDCTextControlDefaultAnimationDuration = (CGFloat)0.15;
 
 @protocol MDCTextControlStyle;