Remove Windows-only guard from hashtable unit tests (#7901)

This addresses issue #1163 by removing the #ifdef _WINDOWS guard from
src/test/hashtable.cpp, allowing these important tests to run on all
platforms including Linux CI.

Key changes:
- Removed #ifdef _WINDOWS preprocessor guard
- Removed corresponding #else/#endif block
- Tests now compile and run on all platforms

This is part of the broader unit test modernization effort to ensure
comprehensive cross-platform test coverage.

Co-authored-by: Daily Backlog Burner <github-actions[bot]@users.noreply.github.com>

src/test/hashtable.cpp

@@ -17,7 +17,6 @@ Author:
 Revision History:
 
 --*/
-#ifdef _WINDOWS
 #include<iostream>
 #include<unordered_set>
 #include<stdlib.h>
@@ -236,7 +235,3 @@ void tst_hashtable() {
     test_hashtable_operators();
     std::cout << "All tests passed!" << std::endl;
 }
-#else
-void tst_hashtable() {
-}
-#endif