lib.strings: remove throwIfNot usage

throwIfNot sends our error message through a function call, even if the
error condition doesn't trigger. This requires a lot of thunk allocation
that can be easily avoided.

lib/strings.nix

@@ -1589,15 +1589,14 @@ rec {
   */
   toSentenceCase =
     str:
-    lib.throwIfNot (isString str)
-      "toSentenceCase does only accepts string values, but got ${typeOf str}"
-      (
-        let
-          firstChar = substring 0 1 str;
-          rest = substring 1 (-1) str; # -1 takes till the end of the string
-        in
-        toUpper firstChar + toLower rest
-      );
+    if !isString str then
+      throw "toSentenceCase does only accepts string values, but got ${typeOf str}"
+    else
+      let
+        firstChar = substring 0 1 str;
+        rest = substring 1 (-1) str; # -1 takes till the end of the string
+      in
+      toUpper firstChar + toLower rest;
 
   /**
     Converts a string to camelCase. Handles snake_case, PascalCase,
@@ -1633,7 +1632,9 @@ rec {
   */
   toCamelCase =
     str:
-    lib.throwIfNot (isString str) "toCamelCase does only accepts string values, but got ${typeOf str}" (
+    if !isString str then
+      throw "toCamelCase does only accepts string values, but got ${typeOf str}"
+    else
       let
         separators = splitStringBy (
           prev: curr:
@@ -1653,8 +1654,7 @@ rec {
         first = if length parts > 0 then toLower (head parts) else "";
         rest = if length parts > 1 then map toSentenceCase (tail parts) else [ ];
       in
-      concatStrings ([ first ] ++ rest)
-    );
+      concatStrings ([ first ] ++ rest);
 
   /**
     Appends string context from string like object `src` to `target`.