VFPU: Drop the inaccurate dot product paths

- Fixes #12082

The bit-exact VFPU dot product is the default everywhere and fast enough,
so the plain multiply-add paths in the interpreter and the IR frontend go,
along with the AccurateVdot setting, --accurate-vdot, the ForceAccurateVdot
compat flag and the Vec4Dot IR op, which nothing emits any more.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Core/CmdLine.cpp

@@ -199,7 +199,6 @@ static const CommandLineParam g_autoParams[] = {
 	{POFF(compare), CmdParamType::Bool, "compare", 'c', "Enable comparison mode", CmdLineMode::Headless},
 	{POFF(bench), CmdParamType::Bool, "bench", 'b', "Enable benchmark mode", CmdLineMode::Headless},
 	{POFF(oldAtrac), CmdParamType::Bool, "old-atrac", '\0', "Use old ATRAC decoder"},
-	{POFF(accurateVdot), CmdParamType::Bool, "accurate-vdot", '\0', "Compute VFPU dot products bit-exactly like the PSP (default; =false for the faster approximation)"},
 	{POFF(jitProfile), CmdParamType::String, "jit-profile", '\0', "Profile the CPU core and write its hottest blocks to FILE on exit"},
 	{POFF(memStickInserted), CmdParamType::BoolInverse, "no-memstick", '\0', "Run with the memory stick removed"},
 	{POFF(log), CmdParamType::String, "log", '\0', "Output log to FILE", CmdLineMode::Application},
@@ -632,10 +631,6 @@ void CommandLineOptions::ApplyToConfig() const {
 		g_Config.bUseOldAtrac = oldAtrac.value();
 		g_Config.DoNotSaveSetting(&g_Config.bUseOldAtrac);
 	}
-	if (accurateVdot.has_value()) {
-		g_Config.bAccurateVdot = accurateVdot.value();
-		g_Config.DoNotSaveSetting(&g_Config.bAccurateVdot);
-	}
 	if (jitProfile.has_value()) {
 		g_Config.sJitProfileFile = jitProfile.value();
 	}