Remove some #warnings

There surely will be someone integrating the SDK via source, use iOS 7 as base SDK and enabled to treat warnings as errors.

Classes/BITAppStoreHeader.h

@@ -35,9 +35,6 @@
 #define __IPHONE_6_1     60100
 #endif
 
-#if __IPHONE_OS_VERSION_MIN_ALLOWED > __IPHONE_6_1
-#warning Remove the option to adjust the button style. We are now iOS 7 only.
-#endif
 
 /**
  * Header style depending on the iOS version

Classes/BITHockeyBaseManager.m

@@ -43,10 +43,6 @@
 #import <mach-o/ldsyms.h>
 #endif
 
-#if __IPHONE_OS_VERSION_MIN_ALLOWED > __IPHONE_6_0
-#warning The following ifndef can be removed
-#endif
-
 #ifndef __IPHONE_6_1
 #define __IPHONE_6_1     60100
 #endif
@@ -104,9 +100,6 @@
   return (_appIdentifier ? bit_URLEncodedString(_appIdentifier) : bit_URLEncodedString([self mainBundleIdentifier]));
 }
 
-#if __IPHONE_OS_VERSION_MIN_ALLOWED > __IPHONE_6_1
-#warning Support for pre iOS 7 systems can be removed!
-#endif
 - (BOOL)isPreiOS7Environment {
   static BOOL isPreiOS7Environment = YES;
   static dispatch_once_t checkOS;

Classes/BITStoreButton.h

@@ -52,10 +52,6 @@
 #define __IPHONE_6_1     60100
 #endif
 
-#if __IPHONE_OS_VERSION_MIN_ALLOWED > __IPHONE_6_1
-#warning Remove the option to adjust the button style. We are now iOS 7 only.
-#endif
-
 /**
  * Button style depending on the iOS version
  */