patch 8.1.0773: not all crypt code is tested

Problem:    Not all crypt code is tested.
Solution:   Disable unused crypt code.  Add more test coverage.
diff --git a/src/crypt.c b/src/crypt.c
index 5996070..f82ee7b 100644
--- a/src/crypt.c
+++ b/src/crypt.c
@@ -34,7 +34,9 @@
     char    *magic;	/* magic bytes stored in file header */
     int	    salt_len;	/* length of salt, or 0 when not using salt */
     int	    seed_len;	/* length of seed, or 0 when not using salt */
+#ifdef CRYPT_NOT_INPLACE
     int	    works_inplace; /* encryption/decryption can be done in-place */
+#endif
     int	    whole_undofile; /* whole undo file is encrypted */
 
     /* Optional function pointer for a self-test. */
@@ -80,7 +82,9 @@
 	"VimCrypt~01!",
 	0,
 	0,
+#ifdef CRYPT_NOT_INPLACE
 	TRUE,
+#endif
 	FALSE,
 	NULL,
 	crypt_zip_init,
@@ -95,7 +99,9 @@
 	"VimCrypt~02!",
 	8,
 	8,
+#ifdef CRYPT_NOT_INPLACE
 	TRUE,
+#endif
 	FALSE,
 	blowfish_self_test,
 	crypt_blowfish_init,
@@ -110,7 +116,9 @@
 	"VimCrypt~03!",
 	8,
 	8,
+#ifdef CRYPT_NOT_INPLACE
 	TRUE,
+#endif
 	TRUE,
 	blowfish_self_test,
 	crypt_blowfish_init,
@@ -167,6 +175,7 @@
     return -1;
 }
 
+#ifdef CRYPT_NOT_INPLACE
 /*
  * Return TRUE if the crypt method for "method_nr" can be done in-place.
  */
@@ -175,6 +184,7 @@
 {
     return cryptmethods[state->method_nr].works_inplace;
 }
+#endif
 
 /*
  * Get the crypt method for buffer "buf" as a number.
@@ -366,6 +376,7 @@
     vim_free(state);
 }
 
+#ifdef CRYPT_NOT_INPLACE
 /*
  * Encode "from[len]" and store the result in a newly allocated buffer, which
  * is stored in "newptr".
@@ -422,6 +433,7 @@
     method->decode_fn(state, ptr, len, *newptr);
     return len;
 }
+#endif
 
 /*
  * Encrypting "from[len]" into "to[len]".
@@ -436,6 +448,7 @@
     cryptmethods[state->method_nr].encode_fn(state, from, len, to);
 }
 
+#if 0  // unused
 /*
  * decrypting "from[len]" into "to[len]".
  */
@@ -448,6 +461,7 @@
 {
     cryptmethods[state->method_nr].decode_fn(state, from, len, to);
 }
+#endif
 
 /*
  * Simple inplace encryption, modifies "buf[len]" in place.