patch 9.0.0265: no good reason why the "gf" command isn't in the tiny version

Problem:    No good reason why the "gf" command is not in the tiny version.
Solution:   Graduate the file_in_path feature.

src/option.h

@@ -780,9 +780,7 @@ EXTERN char_u	*p_pex;		// 'patchexpr'
 #endif
 EXTERN char_u	*p_pm;		// 'patchmode'
 EXTERN char_u	*p_path;	// 'path'
-#ifdef FEAT_SEARCHPATH
 EXTERN char_u	*p_cdpath;	// 'cdpath'
-#endif
 #if defined(DYNAMIC_PERL)
 EXTERN char_u	*p_perldll;	// 'perldll'
 #endif
@@ -908,9 +906,7 @@ EXTERN int	p_si;		// 'smartindent'
 EXTERN int	p_sta;		// 'smarttab'
 EXTERN long	p_sts;		// 'softtabstop'
 EXTERN int	p_sb;		// 'splitbelow'
-#if defined(FEAT_SEARCHPATH)
 EXTERN char_u	*p_sua;		// 'suffixesadd'
-#endif
 EXTERN int	p_swf;		// 'swapfile'
 #ifdef FEAT_SYN_HL
 EXTERN long	p_smc;		// 'synmaxcol'
@@ -1196,9 +1192,7 @@ enum
     , BV_SPO
 #endif
     , BV_STS
-#ifdef FEAT_SEARCHPATH
     , BV_SUA
-#endif
     , BV_SW
     , BV_SWF
 #ifdef FEAT_EVAL