wasip1: deduplicate target selection

Before this change, `GOOS=wasip1 GOARCH=wasm` and `-target=wasip1` were
entirely separate configurations that just happened to be the same in
practice. This change makes sure we keep only one of them to avoid
inconsistencies.

targets/wasi.json

@@ -1,3 +0,0 @@
-{
-    "inherits": ["wasip1"]
-}

targets/wasip1.json

@@ -1,26 +0,0 @@
-{
-	"llvm-target":   "wasm32-unknown-wasi",
-	"cpu":           "generic",
-	"features":      "+bulk-memory,+mutable-globals,+nontrapping-fptoint,+sign-ext",
-	"build-tags":    ["tinygo.wasm"],
-	"goos":          "wasip1",
-	"goarch":        "wasm",
-	"linker":        "wasm-ld",
-	"libc":          "wasi-libc",
-	"rtlib":         "compiler-rt",
-	"scheduler":     "asyncify",
-	"default-stack-size": 65536,
-	"cflags": [
-		"-mbulk-memory",
-		"-mnontrapping-fptoint",
-		"-msign-ext"
-	],
-	"ldflags": [
-		"--stack-first",
-		"--no-demangle"
-	],
-	"extra-files": [
-		"src/runtime/asm_tinygowasm.S"
-	],
-	"emulator":      "wasmtime --dir={tmpDir}::/tmp {}"
-}